JP2811533B2 - Control method of injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control system for an injection molding machine, and more particularly to a control system capable of improving the operability of an operator.

[0002]

2. Description of the Related Art In general, injection molding of a resin product is performed in a process of plasticizing resin, filling, holding pressure, and cooling. In order to obtain high quality molded products, in addition to controlling the temperature of the mold consisting of the fixed mold and the movable mold, the resin temperature in the mold, the injection pressure, etc., the mold clamping force on the mold and the mold It is important to control the opening amount, that is, the distance between the mold parting surfaces, and to switch from the filling process to the pressure-holding process, that is, to set the timing of VP switching.

[0003]

As for the control of the mold clamping force, the set value F (ton) of the mold clamping force is expressed as F = A · P / 1.
It is generally calculated based on the formula of 000, and until now, an injection process including a filling process and a pressure holding process,
The mold clamping force in the cooling process is kept constant. A is the pressure receiving area of the molded product (cm ² ), and P is the average internal pressure of the mold (k
g / cm ² ). However, if the mold clamping force is set high in such a control method, air generated from the air or molten resin in the mold when the resin is filled in the mold will cause the mold to die at the end of the injection process. When compressed and remains in the mold without being discharged from the mold, defects such as short shots, welds, and burns are caused. In this case, the operator operates to lower the set value of the mold clamping force in order to easily discharge air and gas in the mold. However, if the set value is too low, burrs are likely to be generated. Problems arise.

On the other hand, regarding the switching from the filling process to the pressure-holding process, the timing of switching from the filling process to the pressure-holding process is set based on the experience of the operator. It is difficult to set the optimal switching timing because it changes depending on the mold and the die structure.

Next, measures for preventing burr generation in the pressure holding step will be described. Normally, immediately after switching from the filling process to the pressure-holding process, resin filling into the mold is almost complete, so the force to open the parting surface between the fixed mold and the movable mold is low. Acts to generate a small mold opening. If the force for opening the parting surfaces by the injection pressure is larger than the mold clamping force, the mold opening amount increases, and as a result, burrs occur. Therefore, the operator increases the set value of the mold clamping force or changes the set value of the injection condition so that the injection pressure does not become excessive.

However, in the method of maintaining the mold clamping force constant during the injection process as described above, increasing the mold clamping force unnecessarily increases the air and gas escape in the mold as described above. Causes short shots, welds, burns, and other defects. Also, when changing the injection conditions, it is necessary to rely on the experience of the operator, and it takes a long time to determine the conditions. Furthermore, even after finding the condition of a non-defective product, the optimum balance between injection and mold clamping may be lost due to a temperature fluctuation of a resin, a mold or the like, and a defective product may be generated.

The injection compression molding method will be described. In the case of general injection compression, the compression drive source is almost always a hydraulic mechanism for clamping or a hydraulic mechanism connected to a movable platen provided with a movable mold. is there. In any of the configurations, the compression start timing is based on timer control from the filling start time, the pressure holding start time, or the switching time from the filling process to the pressure holding process, but it is difficult to set an optimal timer time. On the other hand, the compression pattern generally changes stepwise, and in order to realize an optimal compression pattern for the type of resin and the shape of the mold, multiple settings are required, and the setting takes a long time. . Furthermore, there is a problem that the behavior of the actual compression pressure cannot follow the stepwise setting, and differs from the behavior intended by the operator, or changes due to fluctuations in the operating oil temperature of the hydraulic mechanism.

In view of the above problems, a main object of the present invention is to provide an injection molding machine capable of minimizing the work of determining and inputting various set values, which has been performed based on the experience of an operator. It is to provide a control method.

Another object of the present invention is to provide a control method of an injection molding machine which is effective in preventing short shots, welds, burns, and the occurrence of defects such as burrs and sink marks.

[0010]

According to the present invention, there is provided a stationary mold attached to a fixed platen, a movable mold attached to a movable platen, and the stationary mold and the movable mold driven by driving the movable platen. And a distance sensor for detecting the distance L between the platens of the two platens, and a clamping pressure by the driving source as a mold clamping force. A pressure sensor for detecting, and a control unit for controlling the drive source using a distance detection signal from the distance sensor and a pressure detection signal indicating the mold clamping force from the pressure sensor, and the like. The unit controls the drive source so that the distance between the platens becomes a constant value L _O during the filling process when the filling of the resin is started. Set Switching from the filling process to the pressure-holding process when reaching the set position, and controlling the driving source so as to maintain the mold clamping force at the time of switching to the pressure-holding process when the pressure-holding process is started. Then, as a result of the progress of resin filling, when the distance between the platens increases and reaches the first value L _S ,
Controlling the drive source such that the inter-platen distance thereafter follows a predetermined change pattern having a second value L _E as an arrival point; and setting the inter-platen point distance to the second value L _E. If met, the mold clamping force at that time to control said driving source so as to maintain a predetermined time after the predetermined time follows the descending pattern distance between the platen and point reaches a predetermined value L _M and controlling the driving source so, the platen distance is and executes the step of terminating said pressure-holding step and reaches the predetermined value L _M.

In addition, instead of the step of monitoring the screw position and switching from the filling step to the pressure holding step,
A step of monitoring the resin pressure in the nozzle portion or the mold and switching from the filling step to the pressure holding step when the resin pressure reaches a predetermined value may be executed.

Further, instead of the step of monitoring the position of the screw and switching from the filling step to the pressure holding step,
A step of monitoring the oil pressure of the injection cylinder and switching from the filling step to the pressure holding step when the oil pressure reaches a predetermined oil pressure may be executed.

Further, in place of the step of monitoring the screw position and switching from the filling step to the pressure holding step,
A step of monitoring the elapse of time from the start of filling and switching from the filling step to the pressure holding step when a predetermined time has elapsed from the start of filling may be executed.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of an injection device and a mold clamping device in an injection molding machine to which the present invention is applied. In the injection device, the resin injected from the hopper 11 is measured and kneaded with the screw 13 while being melted in the heating cylinder 12, and the molten resin is stored in front of the screw 13. The stored resin is passed through the nozzle 16 by moving the screw 13 forward, that is, to the mold side by a hydraulic cylinder mechanism including an injection cylinder 14 and a piston 15 so that the fixed mold 1
The cavity formed by the mold 7 and the movable mold 18 is filled. Drive oil whose flow rate or pressure is controlled flows into and out of the injection cylinder 14 through the inflow / outflow section 14-1 in accordance with the filling and pressure keeping processes.

On the other hand, the mold clamping device is fixed to a frame (not shown), and a rear platen 22 has four tie bars 23 (2 in the figure) with respect to a fixed platen 21 having a fixed mold 17.
(Only the book is shown). A hydraulic piston 25 is disposed in a hydraulic cylinder 24 fixed to the rear platen 22, and a movable platen 26 to which the movable mold 18 is fixed is connected to the hydraulic piston 25.
The movable platen 26 is configured to be slidable on the tie bar 23 with the movement of the hydraulic piston 25. That is, the movable platen 26 moves in the mold closing direction when the driving oil is injected from the inflow / outflow portion 24-1 of the hydraulic cylinder 24 through a pressure control valve (not shown), and moves in the mold opening direction when the driving oil is injected from the inflow / outflow portion 24-2. Moving.

The hydraulic cylinder 24 is provided with a pressure sensor 27 for detecting a hydraulic pressure as a mold clamping force, and when the mold is closed, the hydraulic pressure in the hydraulic cylinder on the inflow / outflow section 24-1 side is determined. The mold clamping force can be controlled by adjusting based on the detection value of the pressure sensor 27. The fixed platen 21 and the movable platen 26 are provided with a distance sensor 28 for detecting a distance L between the platens.
And the delicate opening between the parting surfaces of the movable mold 18 and the movable mold 18 can be measured. The distance between the platens referred to here means the distance between the parting surfaces, a mold thickness or a partial mold thickness including a so-called mold opening amount, and the behavior is almost the same as the behavior of the mold opening amount. It is.

Although not shown in the drawing, the injection device and the mold clamping device, in addition to the pressure sensor 27 and the distance sensor 28, a screw position sensor for detecting the screw position, the inside of the nozzle 16 or the mold Various sensors such as a resin pressure sensor for detecting a resin pressure in the inside, an injection pressure sensor for detecting a hydraulic pressure of the injection cylinder 14, and the like are provided.

2 and 3 show examples of a laser type and an eddy current type distance sensor, respectively. The laser distance sensor shown in FIG. 2 includes a laser head 28-1 for laser transmission and reception provided on the fixed platen 21 and a reflector 28-2 for laser reflection provided on the movable platen 26. A detection signal of the distance between the platens is transmitted from 1 to a control unit described later. Such a laser method has a long measurement span and can measure up to the maximum mold opening. The laser head 28-1 and the reflector 28-2 are not fixed molds 17 and movable molds 18, but are fixed platens. 21, because it is installed on the movable platen 26,
Adjustment of the distance sensor is unnecessary even when the mold is replaced.

On the other hand, even if the measurement span is short as in the eddy current method, if the sensor unit 31 is mounted on the mounting table 30 having a variable stroke, when the mold is replaced, the mold is closed. In this state, it is only necessary to adjust the sensor unit 31 so that it is within the measurement span.

In any case, as compared with a system in which the sensor is directly mounted on the mold, there is no need for the mold to have a special structure for installing the sensor, and an existing mold having no structure for mounting the sensor. However, since it can be used as it is, the workability of mold replacement is improved, and the cost of the mold can be reduced.

FIG. 4 shows the configuration of a control system required to execute the control method according to the present invention. The control system includes a setting signal from a setting device 41 for inputting a distance between platens, a mold clamping force, and the like, a pressure detection signal from a pressure sensor 27, a distance detection signal between platens from a distance sensor 28, and various signals described above. Sequence processing and function pattern generation of the injection molding machine based on detection signals from the sensor, etc.
And a memory 44 for storing data such as a platen distance and a mold clamping force. In addition,
The microprocessing unit 43 also has a time monitoring function using a timer.

FIGS. 5 and 6 are flow charts showing the flow of the control operation from the mold closing to the completion of the pressure holding executed by the control system shown in FIG. 4. The distance L between the platens and the mold clamping force P are shown in FIG. The control operation will also be described with reference to FIG. 7 showing changes in injection speed and pressure.

In step S1, a mold closing operation before starting the molding is performed.

In step S2, the mold closing operation is performed as conventionally performed, the position of the movable platen 26 is measured,
Alternatively, it is determined from the detection signal of the pressure sensor 27 that the mold has been closed. At this time, the fixed mold 17 and the movable mold 1
8 have the minimum clamping force P required to close them.
_I have only received _one .

In step S3, the distance L between the platens when the mold is closed is determined by the microprocessing unit 43.
Is stored in the memory 44 as the initial inter-platen distance L _O.

In step S4, filling of the resin is started.
When the filling is started, in step S5, the microprocessing unit 43 sets the pressure control valve 42 according to the distance L between the platens detected by the distance sensor 28 so that the initial distance L _O between the platens is maintained as a target value. Control and
The mold clamping force P changes accordingly. As described above, the distance between the platens is changed by changing the mold clamping force P to the initial distance L between the platens.
_When filling while maintaining _O , the mold receives only the minimum mold clamping force necessary to close it, so air remaining in the mold and gas generated by the resin are easily discharged, In addition, since the initial distance L _O between the platens is set to the target value, the parting surfaces of the fixed mold 17 and the movable mold 18 do not open even when receiving the filling pressure of the resin, and burrs do not occur. When the mold clamping force P is appropriately changed according to the filling pressure, the movable mold 18 is pressed against the fixed mold 17 in a so-called soft touch state, and air and gas are discharged from the mold. In addition, an effect is obtained that burrs can be prevented while preventing the occurrence of burrs.

In step S6, the microprocessing unit 43 monitors the detection signal from the screw position sensor and determines whether the screw has moved to a predetermined position. Then, when the screw reaches a predetermined position, the process proceeds to step S7 and the VP
Switching, that is, switching from the filling process to the pressure holding process is performed.

The VP switching operation can also be performed by monitoring the detection signal of the above-described resin pressure sensor or injection pressure sensor in the microprocessing unit 43. That is, the microprocessing unit 43 determines whether the resin pressure in the nozzle 16 or the mold has reached a predetermined value since the start of filling, and performs VP switching when the resin pressure reaches the predetermined value. Alternatively, whether the oil pressure in the injection cylinder 14 has risen to a predetermined oil pressure may be monitored, and VP switching may be performed when the oil pressure reaches the predetermined oil pressure. Further, the V-P switching may be performed when a predetermined time has elapsed from the start of filling by the time monitoring function of the timer included in the microprocessing unit 43.

Next, when the switching from the filling process to the pressure holding process is performed, the microprocessing unit 43 stores the mold clamping force P ₂ at the time of the switching in the memory 44 in step S8. Subsequently, in step S9, the micro-processing unit 43 by controlling the pressure control valve 42 the clamping force P ₂ stored as a target value, it operates to maintain the mold clamping force P to the target value P _2. In this state, the resin is almost completely filled in the mold, but since the resin is further filled in the mold by the pressure-holding operation, the pressure in the mold increases and the mold tries to open. . On the other hand, by maintaining the mold clamping force at the target value P ₂ , the mold is intentionally opened as shown in FIG. 7 and the rapid change in the flow of the resin filled in the mold is reduced. As a result, a so-called cushion effect can be obtained that prevents adverse effects such as distortion on the molded product.

In step S10, the distance L between the platens increases as the mold is about to open for the above reason. The microprocessing unit 43 performs an operation of determining whether or not the inter-platen distance L matches a preset limit inter-platen distance L _{S at} which the restriction of the inter-platen distance is to be started, and if they are equal, the process proceeds to step S11.

[0031] In step S11, the micro-processing unit 43, the shape from between the restriction start platen distance L _S to a predetermined end-of-restriction platen distance L _E to generate a smooth function pattern L _P1. The pressure control valve 42 is controlled so that the platen distance L follows the function pattern L _P1 with the value specified by the function pattern L _P1 as a target value, and the mold clamping force P is adjusted.

Examples of the function pattern L _P1, and is, for example, first-order lag function when the L _E> L _S as shown by the solid line in FIG. 8, in the case of the L _E <L _S as indicated by the broken line, for example Exponential function. As described above, in step S11, it is possible to limit the maximum distance between the platens at which burrs do not occur, so that burrs can be prevented from occurring. Also, to control the distance between the platens while suppressing the rapid change of resin flow in the mold with a smooth change pattern, the pressure difference between the area near the gate and the area far from the gate in the mold is reduced. The occurrence of defects such as sink marks and warpage can be prevented.

[0033] Furthermore, restriction start platen distance L _S, restriction ends platen distance L _E, it is possible to arbitrarily change the shape of the function pattern L _P1 depending on the setting of the constant T ₁ when defining the function pattern L _P1 Therefore, the operator can set optimal conditions according to the thickness of the molded product and the type of resin (viscosity, temperature characteristics, solidification speed, etc.). For example, since resin has compressibility, if the thickness of the molded product is thick,
Since the resin is filled even after the distance L between the platens reaches the distance L _S between the limit start platens, it is possible to take a method of gradually opening the mold as L _E > L _S. Conversely, for a thinner one, the filling after the platen distance L reaches the limit starting platen distance L _S is small,
_{As E} <L _S , a method of gradually closing the mold can be adopted.

It should be noted that a plurality of set values of ΔL = L _S −L _E and a plurality of types of time constants T ₁ are set as fixed values and stored in the memory 44, and the operator sets the limit start platen distance L
_{In addition} to setting _S , an optimum value may be selected from these values so that an optimum pattern can be selected.

[0035] In step S12, performs a determination of whether the operation microprocessing unit 43 the values defined by the function pattern L _P1 matches the limit ends platen distance L _E, terminates the generation of the function pattern L _P1 If they match Then, the process proceeds to step S13. In step S13, the micro-processing unit 43 measures the clamping force P ₃ of the generation end of the function pattern L _P1 stored in the memory 44. In step S14, it microprocessing unit 43 is to control the pressure control valve 42 as a target value the Katashimeryoku P ₃ until a predetermined time t1 from the generation end starts time measurement by the timer has elapsed the function pattern L _P1 Accordingly, to perform a control operation for maintaining the clamping force to P _3.

In step S15, the filling of the resin into the mold is reduced as the mold is sealed with the gate as the pressure is maintained. The distance L decreases. in the meantime,
The microprocessing unit 43 monitors whether a predetermined time t1 has elapsed since the start of the timer operation,
When the predetermined time t1 has elapsed, the process proceeds to step S16 to increase the mold clamping force and start injection compression.

By the way, regarding the optimal timing of starting the injection compression, the purpose of the injection compression is to compensate for the shrinkage of the resin of the molded article on the mold clamping side. In this case, if the timing of the compression is too early, the temperature of the resin is high, and a backflow from the gate of the mold to the nozzle side occurs, or the resin in the mold moves to cause sink marks, thereby causing a compression effect. Can not expect. On the other hand, if the timing of the compression is too late, the solidification proceeds on the surface of the molded product in the mold, so that a uniform pressure cannot be applied to the whole. That is, when the compressive force is low, the compressive force cannot be transmitted to a portion where the solidification has not progressed, and when the compressive force is high, the portion where the solidification is progressing is excessively applied to cause distortion.

In step S16, the microprocessing unit 43 sets the minimum inter-platen distance L _M from the current inter-platen distance (the clamping force P
Of up area overlaps with) generates a first-order lag function pattern L _P2 with the goal, platen distance L controls the pressure control valve 42 so as to follow the pattern L _P2. This pattern L _P2 can be arbitrarily set by changing the time constant T ₂ that defines the same as the above-mentioned function pattern L _P1 by the operator, and the time constant T ₂
May be stored in the memory 44 as a plurality of fixed values so that the operator can select an optimum pattern according to the solidification speed of the resin, the shape of the molded product, and the like. Alternatively, the function pattern L _P2 may be a simpler function, for example, a linear function depending on the processing capacity of the microprocessing unit 43.

As described above, in the injection compression according to the present invention, the mold clamping force is controlled so as to change in accordance with a smooth ascending pattern that the drive source can easily follow.
The contraction caused by solidification can be ideally compensated for by the compression operation. Moreover, the setting of the rising pattern can be arbitrarily changed according to the shape of the molded product and the solidification speed of the resin.

[0040] In step S17, the microprocessing unit 43 monitors whether the platen distance matches the prescribed value L _M function pattern L _P2, the pressure-holding step shifts the match to step S18 Complete. This is because the cooling and solidification of the resin in the mold progress from before and after the inflection point in step S15, and the function pattern L _P2
When the platen distance matches the distance L _M between the minimum platen by a gate of the mold is because already made need not be sealed applying a dwell pressure. Therefore, the condition for the completion of the pressure holding can be set at this timing.

Thus, one molding cycle is completed.

Although this embodiment shows an example of a hydraulic molding machine, the present invention is also applicable to a disk molding machine or an electric molding machine. It goes without saying that control is possible not only by pressure but also by making the pressure correspond to current or torque.

[0043]

As described above, according to the present invention, the following effects can be obtained. By installing the distance sensor on the fixed platen and movable platen instead of the mold, not only can the workability of mold replacement be improved, but also the mold structure can be simplified and the mold Such costs can be reduced. Furthermore, existing molds can be used as they are without special modification.

By controlling the distance between the platens and controlling the mold clamping force during the injection process, there is no need to set the timing for ending the pressure holding process. In addition, the setting of the filling step and the dwelling step can be simplified, and the conditions for good products can be determined without relying on the experience of the operator, and the time for that can be shortened.

It is possible to eliminate the occurrence of defects such as burrs, sink marks, warpage, and distortion of the molded product.

A stable behavior of the mold opening amount, the mold clamping force, and the injection compression pressure can be realized for each shot, and the variation between shots of the molded product can be reduced. It is possible to reduce the influence on the molded product due to the fluctuation of the resin, the mold temperature, and the driving oil temperature of the hydraulic cylinder. Since the minimum injection pressure and mold clamping force for obtaining a good product can be realized, energy consumption can be reduced.

Since the molding can be performed at an optimum pressure for the molded product, the life of the molding machine and the mold is extended.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an injection device and a mold clamping device in an injection molding machine to which the present invention is applied.

FIG. 2 is a diagram illustrating an example of a distance sensor used in the present invention.

FIG. 3 is a diagram for explaining another example of the distance sensor used in the present invention.

FIG. 4 is a block diagram showing a schematic configuration of a control system according to the present invention.

FIG. 5 is a flowchart for explaining the first half of the control operation according to the present invention.

FIG. 6 is a flowchart for explaining the latter half of the control operation according to the present invention.

FIG. 7 is a diagram showing changes in the distance between platens, mold clamping force, injection speed and pressure in the course of the control operation according to the present invention.

FIG. 8 is a diagram showing an example of a function pattern for defining a distance between platens generated according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Hopper 12 Heating cylinder 13 Screw 14 Injection cylinder 15 Piston 16 Nozzle 17 Fixed mold 18 Movable mold 21 Fixed platen 22 Rear platen 23 Tie bar 24 Hydraulic cylinder 25 Hydraulic piston 26 Movable platen 27 Pressure sensor 28 Distance sensor

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yoshihiko Nagata 731-1, Naganumahara-cho, Inage-ku, Chiba-shi, Chiba Pref. Within the Chiba Works of Sumitomo Heavy Industries, Ltd. Address 1 Inside the Chiba Works of Sumitomo Heavy Industries, Ltd. (56) References JP-A-7-100883 (JP, A) JP-A-7-10084 (JP, A) JP-A-7-100892 (JP, A) Kaihei 7-195471 (JP, A) UK Patent Application No. 2218033 (GB, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B29C 45 / 57,45 / 64-45/70 B29C 45 / 76-45/80 EPAT (QUESTEL) WPI / L (QUESTEL)

Claims (4)

(57) [Claims] 1. A fixed mold attached to a fixed platen, a movable mold attached to a movable platen, and the movable platen is driven to open and close the fixed mold and the movable mold. A distance sensor for detecting a distance L between the platens of the two platens, a pressure sensor for detecting a clamping pressure by the driving source as a mold clamping force, A control unit that controls the drive source using a distance detection signal from the distance sensor and a pressure detection signal indicating the mold clamping force from the pressure sensor, and the control unit starts filling of the resin. When, during the filling process, and controlling the driving source so that a distance between the platen becomes a constant value L _O, reaches the position of the screw at a position where the screw is predetermined by monitoring A step of switching from a filling step to a pressure-holding step; and entering the pressure-holding step, controlling the drive source so as to maintain the mold clamping force at the time of switching to the pressure-holding step, and resin filling proceeds. As a result, the distance between the platens increases and the first value L _S
When reached, step a, the distance between the platen points the second in which it said platen distance between the subsequent controls the drive source so as to follow the predetermined change pattern to reach point a second value L _E Upon reaching the value L _E,
The clamping force at that time to control said driving source so as to maintain a predetermined time, the after the predetermined time so as to follow the lowering pattern distance between the platen and reaches point a predetermined value L _M drive and controlling the source, the control system of the injection molding machine in which the platen distance is and executes the step of terminating said pressure-holding step and reaches the predetermined value L _M. 2. The control method for an injection molding machine according to claim 1, wherein the step of monitoring the position of the screw and switching from a filling step to a pressure-holding step is replaced with a step of changing a resin in a nozzle or a mold. A method for controlling an injection molding machine, comprising monitoring pressure and executing a step of switching from a filling step to a pressure holding step when the resin pressure reaches a predetermined value. 3. The control method of an injection molding machine according to claim 1, wherein the step of monitoring the position of the screw and switching from a filling step to a pressure-holding step is performed instead of monitoring a hydraulic pressure of an injection cylinder. A control method for an injection molding machine, which executes a step of switching from a filling step to a pressure holding step when the oil pressure reaches a predetermined oil pressure. 4. The control method for an injection molding machine according to claim 1, wherein a time elapsed from the start of filling is monitored in place of the step of monitoring the position of the screw and switching from a filling step to a pressure-holding step. And a step of switching from the filling process to the pressure-holding process when a predetermined time elapses from the start of the filling.