JP2789295B2 - 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 an injection molding machine.

[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 parting surfaces of the mold, and to switch from the filling process to the pressure-holding process, that is, set the timing of the VP switching.

In terms of the mold opening, during the injection process, the distance between the parting surfaces of the fixed mold and the movable mold according to the resin pressure in the mold is detected as the mold opening, and the detected mold opening is detected. The amount is used for controlling injection or mold clamping and for determining the quality of a molded product.

[0004]

Incidentally, sensors for detecting the amount of mold opening are conventionally mounted on a fixed mold and a movable mold. Therefore, special processing for attaching the sensor to each of the fixed mold and the movable mold is required. Even if the sensor can be mounted without special processing on the mold, it is necessary to remove and attach the sensor when replacing the mold, which is a problem in terms of versatility and workability. was there.

[0005] In view of the above problems, an object of the present invention is to provide an injection molding machine which does not require a distance sensor required for control of mold clamping or the like to be mounted on a mold.

[0006]

SUMMARY OF THE INVENTION The present invention provides a stationary mold attached to a stationary platen, a movable mold attached to a movable platen, and a driving mechanism for driving the movable platen to control the stationary mold. In the injection molding machine having a control unit for performing opening and closing with the movable mold and performing mold clamping, the fixed platen and the movable platen may include a part between a parting surface of the fixed mold and the movable mold. A distance sensor for detecting a distance between platens including a distance, wherein the driving device
To detect the mold clamping force applied by the drive mechanism
A pressure sensor for controlling the operation of the platen.
Switching between the distance and the mold clamping force as control targets
The control unit controls the distance at the start of injection.
Distance between the platens based on the detection signal from the separation sensor.
Control to maintain the separation, and then from the pressure sensor
During the filling or dwelling process based on the detection signal of
It is characterized in that control for switching to control of the tightening force is performed.

[0007]

According to the present invention, since the components of the distance sensor are provided on the fixed platen and the movable platen, there is no need to replace the distance sensor when replacing the mold. Moreover, the distance sensor according to the present invention can detect not only the distance between the parting surfaces of the fixed mold and the movable mold, that is, the change in distance including the expansion and contraction of the mold, but also the mold opening amount. It is possible to perform better molding control as compared with a method in which the mold is opened and closed or the mold is clamped using the detected value of the opening amount.

[0008]

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 hydraulic pressure. The pressure sensor 27 detects the hydraulic pressure in the hydraulic cylinder on the inflow / outflow section 24-1 side as a mold clamping force with the mold closed. The mold clamping force can be controlled by making an adjustment based on the value detected by the pressure sensor 27. The fixed platen 21 and the movable platen 26 have a distance L between the platens.
A distance sensor 28 for detecting the distance between the parting surfaces of the fixed mold 17 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,
The behavior is almost the same as the behavior of the mold opening.

FIGS. 2 and 3 show examples of the laser type and eddy current type distance sensors, 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 measuring span is short as in the eddy current method, if the sensor unit 31 is mounted on the mounting base 30 having a variable stroke, the die is closed when the die is replaced. In this state, it is only necessary to adjust the sensor unit 31 so that it is within the measurement span.

[0013] In any case, as compared with the 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 the 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 necessary for executing control of an injection molding machine to which the present invention is applied. This control system performs injection based on a setting signal from a setter 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 the like. A microprocessing unit 43 for performing sequence processing of a molding machine, generating a function pattern, outputting a command value to a pressure control valve 42 for the hydraulic cylinder 24, a memory 44 for storing data such as a distance between platens, a mold clamping force, and the like. Having.

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, wherein the distance L between the platens and the clamping force P are shown. 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 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, resin filling 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.

[0020] In step S6, microprocessing unit 43 monitors the differential value [Delta] P of the clamping force P detected by the pressure sensor 27, performs one of the determining operation if the differential value [Delta] P has exceeded the predetermined value [Delta] P _1. This is because the mold tries to open as the filling progresses and the mold begins to fill with resin, whereas the microprocessing unit 43 uses the pressure control valve 4 to maintain the initial platen distance L _O.
This is because the mold clamping force P is increased by increasing the command value to 2.

[0021] Figure 8 shows the behavior of the differential value [Delta] P and the mold clamping force P, where V-P switching proceeds to step S7 when the differential value [Delta] P has exceeded the predetermined value [Delta] P _1, that the filling process To the pressure holding step. According to such a determination operation, it is possible to accurately detect the filling of the resin in the mold, and it is possible to perform ideal VP switching without a special setting such as a conventional timer. .
It should be noted that the determination of the VP switching timing based on the differential value ΔP of the mold clamping force is, as is apparent from FIG.
May be performed when the increase of the value stops and reaches a certain value. In addition, the reason why the differential value ΔP is used in place of the mold clamping force P itself in the above determination operation is that when the injection condition changes, the value of the mold clamping force P changes, so that the above determination is difficult. When the differential value ΔP is used, its behavior always becomes as shown in FIG. 8B irrespective of the injection condition, and the above-mentioned judgment is possible.

Next, when the switching to the pressure-holding step is carried out from the filling process, step S8 microprocessing unit 43 stores the clamping force P ₂ at the switching point in the memory 44. 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 reasons described above. 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.

[0024] 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 _P. The platen distance L is adjusted clamping force P by controlling the pressure control valve 42 so as to follow the function pattern L _P values defined by the function pattern L _P as a target value.

Examples of the function pattern L _P, and for example a first-order lag function when the L _E> L _S as shown by the solid line in FIG. 9, 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.

[0026] Furthermore, restriction start platen distance L _S, restriction ends platen distance L _E, is possible to arbitrarily change the shape of the function pattern L _P depending on the setting of the constant T ₁ when defining the function pattern L _P 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.
_{In addition} to setting _S , an optimum value may be selected from these values so that an optimum pattern can be selected.

[0028] In step S12, performs a determination of whether the operation value microprocessing unit 43 is defined by the function pattern L _P matches the limit ends platen distance L _E, ends when matching a generation of function patterns L _P 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 _P stored in the memory 44. In step S14, by microprocessing unit 43 controls the pressure control valve 42 a mold clamping force P ₃ as a target value, 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. In addition, the cooling and solidification of the resin in the mold causes the platen to contract due to the shrinkage. The distance L decreases. in the meantime,
The microprocessing unit 43 monitors the twice differential value d ² L / dt ² of the distance L between the platens, and detects the inflection point of the change in the distance L between the platens, that is, the minimum value of the differential value ΔL of the distance L between the platens. And at the time of detection, step S1
Proceed to 6 to increase the mold clamping force and start injection compression. In addition,
The principle of inflection point detection can be determined by the fact that the twice differential value d ² L / dt ^{2 of the} distance L between platens becomes 0, as shown in FIG.

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 product 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 toward the nozzle side occurs, or the resin in the mold moves, causing sink marks and the like. 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.

On the other hand, the present inventor has found that starting the optimum injection compression at the point where the shrinkage of the resin is the most effective has the most effect on the internal stress, transferability, shape, etc. of the molded article. . In step S15, the distance L between the platens
The point where the degree of decrease of the maximum is the largest, that is, the inflection point, is also the timing at which the resin shrinks most during the pressure holding step. From this, according to the inflection point detection method, it is possible to automatically find the optimal start timing of the injection compression.

In step S16, the microprocessing unit 43 generates a first-order lag function pattern P _P aimed at the current clamping force P ₃ to a preset maximum clamping force P _M. controls the pressure control valve 42 so as to follow the pattern P _P. This pattern P
_P, like the functions pattern L _P described above, to the constant T ₂ when defining this can be arbitrarily set by the operator to change, multiple fixing the set value of the constant T ₂ time The values may be stored in the memory 44 so that the operator can select an optimal pattern according to the solidification speed of the resin, the shape of the molded product, and the like. Alternatively, the pattern P _P is, depending on the processing capability of the microprocessing unit 43, a simpler function, for example, may be a linear function.

[0033] At step S17, the micro-processing unit 43, a function pattern P _P at defined clamping force to monitor whether it matches the maximum clamping force P _M, the process proceeds when match in step S18 the pressure-holding Complete the process.
This cooling of the resin in the mold from around the inflection point in step S15, solidification proceeds, at the time when the mold clamping force by the function pattern P _P coincides with the maximum clamping force P _M, the gate of the mold is already This is because there is no need to apply a dwell pressure after being sealed. 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 and 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.

[0036]

As described above, according to the present invention, since the distance sensor is installed not on the mold but on the fixed platen or the movable platen, not only can the workability of mold replacement be improved. The structure of the mold can be simplified, and the cost of the mold can be reduced. Furthermore, existing molds can be used as they are without special modification. In addition, at the start of injection
To maintain the distance between platens based on these detection signals.
Control based on the detection signal from the pressure sensor.
Switch to control of mold clamping force during filling or holding pressure process
The movable mold can be moved over the fixed mold
In other words, it can be pressed in a soft touch state
And while easily discharging air and gas from the mold,
Also has the effect of preventing the occurrence of burrs.
It is.

[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 for explaining an example of a distance sensor according to the present invention.

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

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

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

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

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

FIG. 8 is a diagram showing a change in a mold clamping force and its differential value for explaining the timing of the VP switching shown in FIG. 7;

FIG. 9 is a diagram showing an example of a function pattern for defining a distance between platens generated in an injection molding machine to which the present invention is applied.

FIG. 10 is a diagram for explaining a principle of detecting an inflection point of a change in a distance between platens in a control process of the injection molding machine of 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 Continuation of the front page (56) References JP-A-5-200820 (JP, A) JP-A-4-356342 (JP, A) JP-A-62-290512 (JP, A) JP-A-63-1988 35327 (JP, A) JP-A-4-86211 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B29C 45/03-45 / 13,45 / 17 B29C 45/26- 45/37 B29C 45/64-45/84

Claims (1)

(57) [Claims] 1. A fixed mold attached to a fixed platen, a movable mold attached to a movable platen, and a drive mechanism for driving the movable platen are controlled to open and close the fixed mold and the movable mold. In addition, in the injection molding machine having a control unit for performing mold clamping, the distance between the platens including the distance between the parting surfaces of the fixed mold and the movable mold is detected by the fixed platen and the movable platen. And a distance sensor is provided for the driving mechanism.
A pressure sensor for detecting the applied mold clamping force is provided,
The controller controls the distance between the platens and the mold clamping force.
Switching control can be performed with each of them as a control object.
The control unit responds to the detection signal from the distance sensor at the start of injection.
Based on the control to maintain the distance between the platens,
Thereafter, charging is performed based on the detection signal from the pressure sensor.
An injection molding machine characterized by performing control for switching to control of mold clamping force during a filling or holding pressure process .