JPH0622844B2 - Injection control method and apparatus for injection molding apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an injection molding apparatus such as a plastic injection molding machine or a die casting machine, in which a holding pressure is controlled by a filling control for changing the injection speed in a plurality of stages and a time control. The present invention relates to an injection control method and apparatus for continuously performing a holding pressure control for changing to a plurality of stages.

[Conventional technology]

In an injection molding machine, for example, a plastic injection molding machine equipped with an injection screw and an injection plunger, the injection speed from the start of injection to the completion of filling has a significant influence on the quality of the molded product. Filling control is being performed. In this filling control method, the advance position of the injection screw is detected by detection means such as limit switches, magnetic scales, potentiometers, etc. It controls the forward speed of the screw, and this changes the injection speed from the start of injection to the completion of filling in multiple stages.

However, the injection process also includes a pressure-holding process that compensates for the volume change when the molten resin cools and solidifies after the filling is completed by advancing the injection screw, and the pressure in this pressure-holding process is not appropriate. And a cavity etc. will occur in the product,
It is necessary to control the holding pressure in this holding step.

Therefore, conventionally, it has been proposed and implemented to perform the holding pressure control subsequent to the filling control. This pressure holding control is provided with a timer that starts timing with a signal generated by detecting the pressure of the pressure oil and a pressure control valve arranged in the pressure oil circuit of the injection cylinder, and when filling is completed, When the pressure reaches a predetermined set pressure, the electric circuit is switched and the pressure control valve is operated to switch the hydraulic pressure from the filling pressure to a lower holding pressure, and this holding pressure is maintained while the timer counts. To hold. Further, after that, the holding pressure is switched to a plurality of stages by a timer and a pressure control valve as required.

[Problems to be solved by the invention]

However, in such a conventional injection control method, as described above, the switching from the filling pressure to the holding pressure and the start of the timing of the timer are performed only by detecting that the hydraulic pressure has reached the set pressure. Even if is not completed, if the hydraulic pressure rises due to resistance such as galling of the injection screw to reach the switching set pressure, it will be switched to the holding pressure by falsely detecting that this is the completion of filling, and the timer will count. May be started. Therefore, there is a problem that the quality of the product is deteriorated because the resin is not sufficiently filled.

Further, when the resin is simply poured into the mold cavity in the filling step, the product may have a cavity even if the holding pressure is applied thereafter.

[Means for Solving Problems] In order to solve such problems, in the present invention, as an injection molding method, the tip end portion of the injection melt extruded member has passed a preset position. When the injection pressure reaches the preset pressure for switching to the pack pressure / holding pressure control, and the injection pressure reaches the preset pressure for the switching condition, A predetermined pack pressure higher than the holding pressure is immediately and forcibly applied, and the pack timer starts to be timed, and the pack pressure is applied at the final stage of the filling process from this time to the time when the pack timer times out. When the pack timer times out, the filling control is switched to the pressure holding control.

In addition, the injection molding device includes an injection position detection device, an injection speed and an injection speed switching position setting device, a switching position start point setting device for pack pressure / holding pressure control, and a pressure setting device for switching conditions to pack pressure / holding pressure control. , Pack pressure and holding pressure, pack time and holding pressure switching time setting device, injection speed deceleration state setting device before the switching position start point of pack pressure / holding pressure control, and injection melt extrusion when connected to these A comparator for emitting a position signal and a pressure signal of the member or a member integrated therewith, a flow control valve for the injection cylinder connected to the signal circuit of the comparator, and a pack pressure and a pressure arranged in a hydraulic circuit to the injection cylinder. A pressure control valve capable of setting a holding pressure in a plurality of stages, and a signal from a switching position start point setting device connected to the pressure control valve and the comparator, the comparator switching to the pack pressure / holding pressure control. After obtaining, when the tip of the injection melt extruded member is still in front of the filling completion position, it is detected that the set pressure for the switching condition to the pack pressure / holding pressure control has been reached, and this pack For switching conditions to pressure / holding pressure control, switch to pack pressure higher than the set pressure and holding pressure and command to start timing of pack timer, and command to switch to holding pressure when pack timer times out. The control circuit is configured to operate the pressure control valve, and a timer that starts timing at the same time as this switching and outputs a signal of a plurality of stages corresponding to the pack pressure and a holding pressure of a plurality of stages.

[Operation] When the injection melt extruding member advances with the pressure oil sent to the injection cylinder through the flow control valve, the flow rate is adjusted by the position detection, and the filling speed control is performed to control the advancing speed. When the tip of the injection melt extruding member is near the end of filling and the tip is past the preset position and is still before the filling completion position, the injection pressure is set to the preset value. When the set pressure for switching condition to pack pressure / holding pressure is reached, the pressure oil circuit is switched to the pack pressure control valve side and the hydraulic pressure rises to the specified pack pressure, and at the same time, the timer starts counting and the timer starts. This pack pressure is maintained while the pack time is being timed. After that, after the pack timer times out, the holding pressure is switched in a direction in which the holding pressure is lowered in a plurality of stages by cooperation of the timer and the pressure control valve.

〔Example〕

1 and 2 show an embodiment of an injection molding apparatus shown for explaining an injection control method according to the present invention. FIG. 1 is a schematic configuration diagram of the injection apparatus and its hydraulic circuit diagram, and FIG. It is a longitudinal cross-sectional view of a flow control valve and its hydraulic circuit diagram. In the figure, 1 is a fixed mold fixed to a fixed platen (not shown), and 2 is a movable mold fixed to a movable platen (not shown) and clamped and opened with respect to the fixed mold 1. Between the molds 1 and 2 clamped like
Are formed. Further, a nozzle hole 5 communicating with the cavity 3 by a runner 4 is opened in the fixed mold 1. The injection cylinder 6 formed in a stepped cylindrical shape and the heating cylinder barrel 7 formed in a long cylindrical shape are joined and fixed to the sides of the molds 1 and 2 so that the molds 1 and 2 can be moved near and far. The nozzle 8 at the tip of the heating cylinder barrel 7 engages with the nozzle hole 5 by advancing the whole of them toward the dies 1 and 2 side. Reference numeral 9 denotes a hopper for supplying resin pellets, which is attached to the supply port of the heating cylinder barrel 7.
An injection screw 12 as a melt extruding member penetrates through the inner hole of the heating cylinder barrel 7 and is concentrically formed on a piston rod 11 integrated with a piston 10 that is fitted in the inner hole of the injection cylinder 6 so as to be able to move forward and backward. Connected, piston 10
A port 13 on the head end side and a port 14 on the rod end side are opened on both sides of. A gear 15 fixed to the injection screw 12 in the rotational direction and fitted slidably in the axial direction meshes with a gear on the driving side (not shown). With this configuration, the resin supplied from the hopper 9 into the heating cylinder barrel 7 is melted by heating and is kneaded by the rotation of the injection screw 12 driven from the gear 15 side, and the control described below is performed. The injection screw 12 is advanced by the pressure oil supplied to the injection cylinder 6 controlled by the apparatus, and the melted and kneaded resin is extruded from the nozzle 8 and injected into the cavity 3.

Therefore, the hydraulic circuit of the injection cylinder 6 and the injection control device will be described. Piping 1 connected to each port 13 and 14
6, 17 are respectively connected to both ports of an electromagnetic switching valve 20 having solenoids 18, 19, and the other ports of this electromagnetic switching valve 20 are a hydraulic pump 22 connected to a motor 21 and a tank 23. Respectively connected to. Then, by exciting the solenoid 19, pressure oil is supplied to the port 13 on the head end side of the injection cylinder 6, and oil on the rod end side of the injection cylinder 6 is discharged from the port 14 on the rod end side, so that the piston 10 and the injection screw 12 move forward and the solenoid 18 is excited to supply pressure oil to the port 14 on the rod end side of the injection cylinder 6, and the oil on the head end side of the injection cylinder 6 to the port on the head end side. Thirteen
The piston and the injection screw 12 are configured to retract by being discharged from.

Further, the pipe 16 between the port 13 and the solenoid switching valve 20
2 is provided with a flow rate control valve 24 shown in detail in FIG.

The housing of this flow control valve 24 is a cylindrical casing 2 with a bottom.
5, a motor base 26 joined to the opening end side thereof, and a valve body 27 serving as a valve body joined to the bottom side thereof are formed coaxially and integrally. The motor base 26 is provided with a pulse motor 28 that rotates by an amount corresponding to the command pulse number in response to a rotation command from a control device 52 described later, and its motor shaft 28a is provided in a hollow portion of the motor base 26 so as to project therefrom. Has been done. Reference numeral 29 denotes a ball screw as a screw mechanism for converting the rotation of the motor shaft 28a into an axial motion, and includes a screw shaft 30 pivotally supported by the motor base 26. The shaft 30 and the motor shaft 28a are connected by a coupling 31. The ball screw 29 includes a bottomed cylindrical nut 33 screwed through a ball 32 to a threaded portion of a screw shaft 30 that faces the inner hole of the casing 25. By rotating respectively to and, nut 3
3 moves backward in the direction of the valve body 27 or the pulse motor 2
It is configured to move forward in eight directions. 34 is a permanent magnet mounted on the peripheral surface of the nut 33, and 35 is a proximity switch that is sensitive to movement of the permanent magnet 34.
3 and a position detector for accurately detecting the moving distance of the spool 38 in the axial direction, which will be described later, and feeding it back to the control device 52, which will be described later. This is a key for restricting the rotation of 33.

A cylindrical sleeve 37 is integrally fitted to the valve body 27, and a spool 38 that is fixed to the nut 33 and moves forward and backward integrally with the nut 33 is attached to the sleeve 37.
Are fitted. The spool 38 includes a drive rod 39 fixed to a nut 33 and slidably supported on the casing 25, and a spool body 40 formed in a cylindrical shape and slidably supported on a sleeve 37. A front chamber 41 and a rear chamber are separated by a spool body 40 in an inner hole of a sleeve 37 which is integrally formed in a core and whose both ends are closed by the valve body 27 and the casing 25.
43 is located near the outer peripheral surface of the spool 38 and is located in the front chamber 41.
And the rear chamber 42 are communicated with each other.
The central portion of 3 is communicated with an annular passage 44 that opens to the circumferential surface of the spool body 40. On the other hand, the inner peripheral surface of the valve body 27 is provided with an annular groove 45 formed in an annular shape so as to extend over the entire circumference.
In FIG. 7, an annular flow path 46 that connects the front chamber 41 and the annular groove 45 by retracting the spool 38 in the direction of the motor 28 from the illustrated position, and an annular flow path 47 that connects the passage 44 and the annular groove 45. And are provided before and after. Further, communication between the front chamber 41 and the annular groove 45 or communication between the passage 44 and the annular groove 45 is referred to as opening the valve, and an increase in the communication area is referred to as an increase in valve opening. The direction in which the spool 38 retracts toward the pulse motor 28 is referred to as the opening direction, and the direction in which the spool 38 advances toward the counter motor direction is referred to as the closing direction. The front chamber 41 and the port of the electromagnetic switching valve 20 are connected by a pipe 16, and the same pipe 16 connected to an outflow passage 48 opening to the outside of the valve body 27 is connected to the injection cylinder 6 and a pipe. 17 is connected to the port of the electromagnetic switching valve 20. With this configuration, the solenoid 19 of the electromagnetic switching valve 20 is excited and the pressure oil is guided to the front chamber 41, and at the same time, the pulse motor 28 rotates and the spool 38 advances in the opening direction. The chamber 41 and the annular flow path 46 begin to correspond. Therefore, the pressure oil in the front chamber 41 flows into the annular groove 45 through the annular flow path 46, and at the same time, flows into the annular groove 45 through the communication passage 43 and the passage 44. The passage 44
No flow occurs in the communication passage 43 between the rear chamber 42 and the rear chamber 42.
The pressure oils that have merged in the annular groove 45 are discharged from the outflow passage 48 and sent from the port 13 of the injection cylinder 6 to the head end side through the pipe 16, so that the injection screw 12 advances.

A control device provided between the flow control valve 24 and the injection cylinder 6 which operate in this manner will be described. Position detection is performed on the injection cylinder 6 side by a magnetic scale 49 that is fixed to the piston rod 11 and moves integrally in parallel with the piston rod 11, and a magnetic head 50 that is fixed on the device frame side in correspondence with the magnetic scale 49. A device 51 is provided and is configured to detect the position of the piston rod 11 or the injection screw 12 integral therewith and emit a signal. Reference numeral 52 denotes a control device provided between the injection cylinder 6, the flow rate control valve 24, and a proportional electromagnetic pressure control valve 57, which will be described later, which is electrically connected between the magnetic head 50 and the pulse motor 28. Unit 53 and injection speed and injection speed switching position setting unit 54 electrically connected between the comparator 53, switching position start point setting unit 55 for holding pressure control, and switching to pack pressure / holding pressure control The injection speed deceleration gradient setting device 65 before the position start point is provided, and the injection speed / injection speed switching position setting device 54 includes a plurality of positions for dividing the moving ends of the injection screw 12 and the injection at that time. The speed is set. Further, the switching position start point setting device 55 for switching to the packing pressure / holding pressure control is set to a position slightly before the end of the filling of the resin in the cavity 3 during the filling process, that is, to the packing pressure / holding pressure control. The most front position that is considered to be good (indicated by symbol A in FIG. 3)
Is set. In addition, the injection speed deceleration gradient setting device 65 before the start point of the switching position to the pack pressure / holding pressure control has the above A
Before the point is reached, the injection pressure is once lowered, and at point A, the injection speed is set so that the injection pressure is certainly lower than the set pressure P ₁ for the pressure for switching to the hatch pressure / holding pressure control. Its slope is set to gradually lower. In this case, the point A and the low injection speed at the point A are also set in advance. Therefore, even if the injection speed is changed immediately before entering the deceleration gradient, the injection speed is always automatically set to the predetermined injection speed at the point A. Then, the position detection signal from the magnetic head 50 is compared with the injection speed and the position setting signal from the injection speed position setter 54 by the comparator 53, and when they match, the pulse motor 28 of the injection screw 12 of the injection screw 12 is detected. The speed is configured to be switched according to a predetermined program. Then, as described above, the movement distance of the spool 38 of the flow control valve 24 is fed back from the position detector 35 to the control device 52. The injection speed and the program set in the injection speed switching position setting device 54 are set according to the shape of the cast product, that is, the cavity 3, and are set according to the size of the cross-sectional area of the cavity 3 that changes in the injection direction. To be done.

Further, in the pipe 56 branched from the pipe between the electromagnetic switching valve 20 which is a hydraulic circuit to the injection cylinder 6 and the hydraulic pump 22, a proportional electromagnetic pressure capable of setting the relief pressure of this hydraulic circuit in a plurality of stages. A control valve 57 is provided, and the proportional electromagnetic pressure control valve 57 is electrically connected to the comparator 53 of the control device 52 and also has a timer 58.
Both are electrically connected via the comparator 53. Further, in the pipe 56 to the proportional electromagnetic pressure control valve 57, a pressure detecting device 59 electrically connected to the comparator 53 is arranged, and detects the pressure in the pipe 56 and outputs a signal to the comparator 53. Is configured to transmit to.

Further, in the comparator 53, a pressure determined on the assumption of the hydraulic pressure when the cavity 3 is completely filled with the molten resin, that is, a pressure which may be switched to the packing pressure / holding pressure control (see FIG. 3). The pressure setting device 60 for switching to the pack pressure / holding pressure control, in which the pressure P _{1 at the} point indicated by the symbol B is set, is electrically connected. Further, the comparator 53 has a reference numeral 61.
The pack pressure P _{2, the} holding pressure, the packing time and the holding pressure switching time setting device are electrically connected,
The setter 61 has a pack pressure P _{2 for} resin filling and holding pressure which is slightly higher than the filling pressure, and a holding pressure at the start of the original holding pressure which is considerably lower than the filling pressure. A pressure, a plurality of holding pressures lower than the pressure, and a switching time thereof are set. And
A signal that the tip of the injection screw 12 has passed a predetermined position (point A in FIG. 3) set in the switching position start point setting device 55 for switching to the packing pressure / holding pressure control in advance and the magnetic head 5
After the position signal from 0 coincides and the comparator 53 transmits the signal, the hydraulic pressure in the pipe 56, that is, the pressure detection device 5
When the detected pressure of 9 and the pressure set by the pressure setting device 60 for switching to the packing pressure / holding pressure control coincide with each other and the signal generated by the comparator 50 is transmitted to the proportional electromagnetic pressure control valve 57, the proportional pressure The electromagnetic pressure control valve 57 is actuated, and the hydraulic pressure to the injection cylinder 6 is the pack pressure P ₂ and the holding pressure, and the packing time and the packing pressure switching time setter 61 set at the packing pressure / holding pressure filling control start time. The pack pressure P ₂ once rises. Further, the comparator is configured to transmit to the timer 58 at the same time as transmission to the proportional electromagnetic pressure control valve 57 so that the timer 58 starts counting time. Here, in order to apply the pack pressure P ₂ for a predetermined period of time, it is because the resin is surely and easily filled in every corner of the cavity 3. This is also because the density of the resin filled in the cavity 3 is kept constant, and the product is prevented from forming cavities. That is, here, the pressure P ₂ necessary and sufficient for finally filling the resin is applied, for example, for 1 to 2 seconds to perform the final pushing of the filling step. Of course, when the speed control is switched to the pack pressure / pressure control, the pressure is temporarily increased, an overshoot occurs, surge pressure rises, and burrs are prevented from occurring. Further, after this, when the pack time has timed out, the pack pressure and the holding pressure, and the holding pressure gradually decreases at predetermined time intervals in accordance with the program of the pressure and time set in the pack time and holding pressure time setting device 61. Is switched to. In addition,
The holding pressure is gradually decreased in order to prevent cracks, residual stress, or sink marks from occurring if too much pressure is applied when the molten resin is about to solidify.

The reference numeral 62 in FIG. 1 is a back pressure adjusting device arranged in the pipe between the flow control valve 24 and the port 13, and includes a solenoid switching valve 63 and a relief valve 64. Before the injection, when the resin is extruded between the nozzle hole 5 and the tip of the injection screw 12 and the injection screw 12 retracts, oil is sent to the head end side of the injection cylinder 6 and a back pressure is applied so that the retraction speed is increased. Is configured to control.

The operation of the injection molding apparatus configured as above will be described. After the molds 1 and 2 are clamped, resin is supplied from the hopper 9 into the heating cylinder barrel 7, the nozzle 8 is closed, and the injection screw 12 is rotated by the drive of the gear 15. The resin which is heated and melted in (2) is extruded toward the nozzle 8 side while being kneaded by the injection screw 12. The injection screw 12 is retracted by the pressure of the resin that accumulates in the heating cylinder barrel 7 in order, and is stopped at a predetermined position by a limit switch (not shown). Then, after the nozzle 8 is opened and the solenoid 19 is excited, the pressure oil is sent from the port 13 of the injection cylinder 6 to the head end side via the flow control valve 24, and the injection screw 12 moves forward via the piston 10. The resin is injected into the cavity 3. The magnetic scale 49 also moves forward with the advance of the injection screw 12, and the magnetic head 50 detects and transmits this each time the injection screw 12 reaches a predetermined position. The injection speed and the injection speed switching setter 54 are programmed in advance. Since the injection speed switching position of multiple stages and the injection speed at that time are set according to
The transmission by this set value and the transmission from the magnetic head 50 are compared by the comparator 53, and are transmitted toward the pulse motor 28 of the flow control valve 24. As a result, as described above, the flow rate of the pressure oil discharged from the flow rate control valve 24 is adjusted for each transmission, and the forward speed of the injection screw 12 is controlled according to the program. Then, the resin injected from the nozzle 8 by the injection screw 12 is filled into the cavity 3 via the runner 4. Shortly before the cavity 3 is filled with resin, the tip of the injection screw 12 is
Switching to holding pressure control When approaching a predetermined position (point A in FIG. 3) preset in the start point setting device 55, when a certain point on the predetermined injection speed deceleration gradient is reached, the injection speed Decreases along this injection speed deceleration slope,
When the point A is reached, the injection speed becomes a predetermined low speed. In this case, when the injection speed reaches the injection speed deceleration gradient, the injection resistance also decreases as the injection speed decreases, and as a result, the injection pressure decreases to some extent. Then, when the tip of the injection screw 12 reaches the point A, the injection pressure surely becomes lower than the set value P _{1 of the} pressure for the switching condition to the pack pressure / holding pressure control. Therefore, even if the injection pressure at the injection speed immediately before reaching the injection speed deceleration gradient is considerably high and is higher than the set value P ₁ of the switching condition pressure to the pack pressure / holding pressure control, Since the injection pressure is once lowered by consciously lowering the injection speed, it is possible to surely set the pressure P ₁ for switching the pack pressure / holding pressure control after point A. Then, when the point A is reached, it is possible to prevent the holding pressure from being changed only by the sudden position control so that the injection product is not deformed or warped.

After passing point A, the comparator 53 outputs a signal, but this alone does not switch the control circuit, and after this value, the resin filling approaches the end and the pressure in the hydraulic circuit shifts to the pack pressure / holding pressure control. Established pressure P ₁ for pack pressure / holding pressure switching condition preset in the pressure setting device 60 for switching condition (see B in FIG. 3).
(Shown in the position), the comparator 53 sends a signal to activate the proportional electromagnetic pressure control valve 57, and immediately, the pack pressure P higher than the set pressure P ₁ for the pack pressure / holding pressure switching condition is reached.
At the same time as ₂ , the timer 58 starts counting time. At this time, the pack pressure P ₂ acts for a required predetermined period of time, for example, 1 to 2 seconds, so that a necessary and sufficient filling pressure acts on the resin without causing burr and the resin is Every corner of the cavity 3 is filled gently. Moreover, the density of the filled resin becomes constant. When the pack pressure action time has passed, the proportional electromagnetic pressure control valve 57 is actuated to discharge the pressure oil to the tank 23, and the hydraulic pressure to the injection cylinder 6 is reduced to the original holding pressure. Then, this pressure is held while the timer 58 is counting,
Thereafter, every time the timer 58 measures a predetermined time, the proportional electromagnetic pressure is supplied via the comparator 53 according to the packing pressure and the holding pressure, and the packing time and the holding pressure switching time setter 61 according to the pressure values of a plurality of stages. A signal is transmitted to the control valve 57, and the holding pressure is sequentially switched to the lower side. Since the resin is solidified and cooled under a predetermined holding pressure by performing the holding pressure control in this manner, the mold is opened and the product is taken out from the injection screw 12 after a predetermined time has elapsed.
One injection cycle is completed by retracting.

At the point where the filling control process is switched to the pack pressure / holding pressure control process (point B in FIG. 3), even if the opening degree of the flow rate control valve 24 is left unchanged, the resin inside the cavity 3 will be considerably damaged. Due to the filling, the injection screw 12 advances only about several mm, and the advancing speed of the injection screw 12 becomes almost zero. However, this is because the opening degree of the flow rate control valve 24 is greatly changed according to the switching point B to the pack pressure / holding pressure control for the purpose of energy saving or the timing of the timer 58 in the subsequent pack pressure / holding pressure control process. It can be made smaller.

FIG. 3 is a relationship diagram of the speed of the injection screw 12, the injection stroke, the hydraulic pressure, and the time in the pack pressure control and the holding pressure control performed at the end of the filling control and the filling process. The injection stroke S was taken in the filling step, and the time T was taken in the packing pressure control step and the holding pressure control step.
In addition, the injection screw 1 is provided in the upper half and the lower half of the vertical axis, respectively.
The injection speed V and the hydraulic pressure P of 2 are shown. In the figure, as described above, in the filling step, the speed of the injection screw 12 is detected in a plurality of stages by detecting the position of the injection screw 12, and near the end of the filling, the injection speed is reduced by a predetermined gradient, and the packing speed is reduced. In the pressure step and the pressure holding step, the holding pressure is controlled in a plurality of stages after the action of the pack pressure P ₂ corresponding to the final injection filling pressure or the injection set pressure every time the timer 58 measures. The switching from the injection speed control process section of the filling process to the pack pressure action process of the last part of the filling process is not performed immediately even when the tip of the injection screw 12 reaches the preset position A, and this A It is performed at the point B when the hydraulic pressure P reaches a predetermined switching pressure P _{1 which} has been set in advance when the point is a little past the point and is still before the filling completion position. Then, after the pack pressure P ₂ acts for a predetermined time, the original holding pressure is controlled in multiple stages as described above.

The dotted line in the figure shows the rising line of the hydraulic pressure when switching is not performed, and when setting the switching pressure P ₁ and the pack pressure P ₂ , this is the absolute pressure P ₃ at the virtual C point. It is necessary to set it so that it does not exceed.

Although the magnetic scale 49 and the magnetic head 50 are illustrated as the position detection device of the injection screw 12 in the present embodiment, a limit switch or a potentiometer may be used. Further, in the present embodiment, an example in which the present invention is applied to a screw type injection molding machine for plastics is shown, but the present invention can also be applied to a plunger type injection molding machine and a die casting machine.

Further, in the present embodiment, the injection speed deceleration gradient is provided before starting the switching position to the pack pressure / pressure holding control, and the deceleration is performed along the injection speed deceleration gradient. Even if the deceleration gradient does not exactly coincide with the deceleration gradient, the deceleration gradient can be gradually decelerated step by step, and as a result, the pressure can be lowered to a predetermined pressure at the point A.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, as the injection molding method of the injection molding apparatus, the tip end portion of the injection melt extruded member is past the preset position and is more than the filling completion position. When the injection pressure reaches the preset pressure for switching to pack pressure / holding pressure control, the injection pressure is higher than the preset pressure for switching condition and the holding pressure. Immediately forcibly apply a predetermined pack pressure and start timing the pack timer, and continue to apply the pack pressure at the final stage of the filling process from this time to the time when the pack timer times out, and the pack timer When the time-out occurs, the filling control is changed to the pressure holding control, and the device is configured to include an injection position detection device, an injection speed and an injection speed switching position setter, a pack pressure / Start position setter for switching to pressure control, pressure setter for switching conditions to pack pressure / holding pressure control, pack pressure / holding pressure, pack time / holding pressure switching time setter, pack pressure / holding control The injection speed deceleration state setting device before the switching position starting point of, and the comparator which is connected to these to generate the position signal and the pressure signal of the injection melt extruded member or the member integrated with this, and the signal circuit of this comparator. A flow control valve for the connected injection cylinder,
A pressure control valve, which is arranged in a hydraulic circuit to the injection cylinder and is capable of setting a pack pressure and a holding pressure of a plurality of stages, is connected to the pressure control valve and the comparator, and the comparator controls the pack pressure and the holding pressure. Switching position to pressure control After the signal from the start point setter is received, when the tip of the injection melt extruding member is still in front of the filling completion position, for switching conditions to pack pressure / holding pressure control Detecting that the set pressure has been reached, commanding switching to a pack pressure higher than the set pressure and pack pressure for switching conditions to this pack pressure / holding pressure control, and the start of the timekeeping of the pack timer, and A control circuit that operates the pressure control valve by instructing switching to pressure holding control when the timer times out, and a multi-stage corresponding to the pack pressure and the multi-stage holding pressure by starting timing at the same time as this switching. The signal of With this configuration, the injection melt extruding member does not malfunction unless the tip end portion of the extruding member extrudes the pressure from the filling pressure to the holding pressure even if the hydraulic pressure rises to the predetermined pressure due to other reasons. Therefore, a sufficient filling pressure is always secured and the quality of the product is improved.

Further, in the present invention, when the injection pressure reaches the predetermined pressure setting for switching pressure maintaining condition within the predetermined injection stroke range because the cavity is almost filled with the resin, the pressure holding control for immediately lowering the pressure is started. Before, at the last stage of the filling process, where the filling is not yet finished, immediately and forcibly, the injection pressure corresponds to the final injection filling pressure or the injection set pressure, which is necessary for the final push-out of the filling process. Since the pack pressure is raised once, the density of the filled resin can be kept constant.

It should be noted that it is possible to greatly increase the control pressure after the tip of the injection melt extruding member reaches the filling completion position, but then the timing is too late, overshooting causes overfilling, wiping burrs, After that, the predetermined holding pressure may not be lowered immediately, and the product weight may vary considerably. However, in the present invention, the control pressure is forcibly increased to act on the pack pressure a few mm before reaching the filling completion position, so that the response is quick and the pressurizing effect by the pack pressure is sufficiently exhibited. Also, there is no overshoot. Therefore, as described above, the product density is almost constant by the action of the push-off force, and as a result, the product weight variation is extremely small. By adopting the present invention, the variation in product weight becomes within 0.2 to 0.3% at most, which is extremely favorable.

In addition, it is possible to easily and reliably fill the resin in every corner of the cavity without scuffing burrs at the time of injection. Therefore, it is always easy to obtain a good-quality injection product without cavities. You can

If an injection speed deceleration state setting device is provided so that the injection speed during the filling process can be set to a predetermined slow injection speed at the start point of the switching position to the pack pressure / holding pressure control, it is possible to The response becomes faster, and more reliable and good results can be obtained.

[Brief description of drawings]

1 to 3 show an embodiment of an injection molding apparatus shown for explaining an injection control method of an injection molding apparatus according to the present invention, and FIG. 1 is a schematic configuration of an injection apparatus of a plastic injection molding machine. Fig. And its hydraulic circuit diagram, Fig. 2 is a longitudinal sectional view of the flow control valve and its hydraulic circuit diagram, and Fig. 3 is a relationship diagram of the stroke and time of the injection screw, and speed and pressure. 6 ... Injection cylinder, 12 ... Injection screw, 22 ... Hydraulic pump, 24 ... Flow control valve, 49 ... Magnetic scale, 50 ... Magnetic head, 51 ... Position detection device, 53 ... Comparator 54 ...... Injection speed and injection speed switching position setter, 55 ...... Switching position start point setter for packing pressure / holding pressure control, 57 …… Proportional electromagnetic pressure control valve, 58 …… Timer, 59 …… Pressure detection device, 60: Pressure conditioner for switching condition to pack pressure / holding pressure control, 61 ... Pack pressure and holding pressure, pack time and holding pressure switching time setter, 65 ... To pack pressure / holding pressure control Injection speed deceleration slope setting device before the switching position start point.

Claims (2)

[Claims] 1. An injection control method for an injection molding apparatus, comprising: a filling control for changing an injection speed to a plurality of stages by a position control; and a holding pressure control for changing a holding pressure to a plurality of stages by a time control. The tip of the extruding member is past the preset position (A) and is still in front of the filling completion position, and the injection pressure (P) is the preset pack pressure. At the time (B) when the set pressure for switching condition (P ₁ ) to the holding pressure control is reached, the set pressure for switching condition (P ₁ ) is set.
And a predetermined pack pressure (P ₂ ) higher than the holding pressure is immediately and forcibly applied, and the pack timer is started to time, and the filling process from this point (B) to the point (C) when the pack timer times out. In the final stage of
An injection control method for an injection molding apparatus, wherein the pack pressure (P ₂ ) is continuously applied, and when the pack timer times out (C), the filling control is shifted to the pressure holding control. 2. An injection position detecting device having a detection end facing a reciprocating path of an injection melt extruding member or a member integrally provided with the injection melt extruding member, and an injection speed and an injection capable of setting a plurality of speeds and positions during an injection stroke. Speed switching position setting device, switching position start point setting device for pack pressure / holding pressure control, pressure setting device for switching conditions to pack pressure / holding pressure control, pack pressure / holding pressure, pack time and holding pressure Pressure switching time setting device, injection speed deceleration state setting device before the switching position start point for pack pressure / holding pressure control, injection position detection position, injection speed and injection speed switching position setting device, pack pressure / holding pressure control Switch position start point setter, pack pressure / holding pressure switching condition pressure setter, pack pressure and holding pressure, pack time and holding pressure switching time setter, injection speed deceleration state setter. A comparator, a flow control valve connected to the signal circuit of the comparator and arranged between the pressure oil source and the injection cylinder, and a pack pressure and a plurality of stages of holding arranged in the hydraulic circuit to the injection cylinder. A pressure control valve capable of setting pressure and pressure, connected to the pressure control valve and the comparator,
After the comparator receives the signal from the switching position start point setting device for the pack pressure / holding pressure control, when the tip of the injection melt extruding member is at a position before the filling completion position, the pack pressure is changed.・ Detecting that the set pressure for the switching condition to the holding pressure control has been reached, and switching to a pack pressure higher than the set pressure for the switching condition to the pack pressure / holding control and the holding pressure and the pack timer A control circuit that operates the pressure control valve by instructing the start of timekeeping and switching to the pressure holding control when the pack timer times out, and is connected to this control circuit and the pressure control valve. An injection control device for an injection molding apparatus, comprising: a timer that starts timing at the same time as switching to the pack pressure / holding pressure control and issues a plurality of stages of signals corresponding to the pack pressure and the plurality of stages of holding pressure.