JP2775580B2 - 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 is particularly effective for preventing the occurrence of defects such as sink marks and warpage.
The present invention relates to a control method that can improve 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 The control of the opening amount, that is, the distance between the mold parting surfaces, the switching from the filling process to the pressure holding process, that is, the timing setting of the VP switching, and the timing of switching to the injection compression molding are important.

[0003]

Among these, the injection compression molding will be described. When the molding process is switched from the filling process to the pressure-holding process and compressed by further applying a mold clamping force, the molded product is less likely to sink even at a low injection pressure. It is known that can be. In the case of general injection compression, the compression drive source is, in most cases, a hydraulic mechanism for mold clamping or a hydraulic mechanism connected to a movable platen provided with a movable mold. In any configuration, the compression pattern set by the operator is generally set in a step-like manner, and multi-stage settings are required to realize an optimum compression pattern for the type of resin and the shape of the mold. And the setting takes a long time. Further, the behavior of the actual compression pressure cannot follow the stepwise setting as shown in FIG. 11 and differs from the behavior intended by the operator, or changes due to fluctuations in the hydraulic oil temperature of the hydraulic mechanism. There was a problem that it would.

In view of the above problems, a main object of the present invention is to provide a control method of an injection molding machine which is effective in preventing occurrence of defects such as sink marks and warpage.

Another object of the present invention is to provide a control method for an injection molding machine capable of minimizing the setting and inputting work of various setting values for injection compression which have been performed based on the experience of an operator. To provide.

[0006]

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. A distance sensor for detecting a distance L between the platens of the two platens, and a clamping pressure for detecting a clamping pressure by the driving source. a pressure sensor, and a control unit for controlling the distance detection signal and the drive source by using the pressure detection signal indicating the clamping force from the pressure sensor from the distance sensor, the control unit, the holding pressure In the process
When it enters, it is accompanied by shrinkage due to cooling and solidification of the resin in the mold
Inflection point is detected in the process of decreasing the interplaten distance L
And starts the injection compression molding and detecting the inflection point, the elevation when <br/> out starts compression molding, the platen distance L between the arrival point a predetermined value L _M, the resin solidification speed, For the shape of molded products
The driving source is controlled so as to follow the smooth falling pattern that has been adjusted .

The controller generates a function pattern whose shape can be arbitrarily changed as the descending pattern.

The control unit may be configured to select the descending pattern from a plurality of predetermined patterns.

[0009]

In the injection compression according to the present invention, the distance L between the platens is controlled to change according to a smooth descent pattern that the drive source can easily follow, and the amount of shrinkage caused by cooling and solidification of the resin is ideally reduced by the compression operation. I can make up for it. This descending pattern can be arbitrarily set and changed according to the shape of the molded product and the solidification speed of the resin.

[0010]

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 side of the inflow / outflow section 24-1 as a mold clamping force in a state where the mold is 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.
The 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 L between the platens can be controlled by adjusting the hydraulic pressure in the hydraulic cylinder based on the detected value of. In addition,
Here, the distance between the platens means the distance between the parting surfaces, that is, a mold thickness or a partial mold thickness including a mold opening amount, and the behavior is almost the same as the behavior of the mold opening amount. .

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 measuring 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.

[0015] In any of the methods, an existing mold that does not have a special structure for mounting the sensor and does not have a structure for mounting the sensor is required as compared with a method in which the sensor is directly mounted on the mold. 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. 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 mold 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 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.

[0022] 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.

FIG. 8 shows the behavior of the mold clamping force P and its differential value ΔP. Here, when the differential value ΔP exceeds a predetermined value ΔP ₁ , the flow shifts to step S7 to switch the VP, ie, 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 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.

[0026] 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.

When L _E > L _{S as} shown by the solid line in FIG. 9, the function pattern L _P1 is, for example, a first-order lag function, and when L _E <L _{S as} shown by the broken line, , For example, an exponential function. Thus, step S1
In No. 1, since the maximum distance between the platens at which burrs do not occur can be limited by setting, the occurrence of burrs can be prevented. 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.

[0028] 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 ΔL = L _S −L _E , a plurality of set values of the time constant T ₁ are set as fixed values and stored in the memory 44, and the operator sets the limit start distance L between the platens.
_{In addition} to setting _S , an optimum value may be selected from these values so that an optimum pattern can be selected.

In step S12, the microprocessing unit 43 performs an operation of determining whether or not the value specified by the function pattern L _P1 matches the limit end platen distance L _E , and if so, ends the generation of the function pattern L _P1. 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.

[0031] 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 mold with the resin is reduced because the mold is sealed with the gate as the pressure is maintained. In addition, the resin in the mold is cooled and solidified. 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, as described above, if the timing of compression is too early, the temperature of the resin is high, and backflow from the gate of the mold to the nozzle side occurs, or sink occurs due to movement of the resin in the mold. Thus, the compression effect cannot be expected. 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.

Steps S14 and S15 are based on the following knowledge. Normally, a force that tries to open the mold by the resin press-fit into the mold cavity from the heating cylinder causes a minute gap (mold opening) Δd between the mold parting surfaces after the resin is full. doing. Then, after the resin is full, the process shifts from the resin compression process to the contraction process. At this time, the internal pressure in the cavity gradually decreases after a sudden rise unless the injection pressure or the mold clamping force is changed suddenly. However, the internal pressure in the cavity is greatly reduced when the resin in the quenching portion pulls the resin in the gradual cooling portion and contracts and solidifies. That is, the decrease rate of the mold opening amount Δd correlated with the acting force increases. In other words, an inflection point also appears in the characteristic curve indicating the relationship between time and the mold opening amount Δd, and this behavior is the same for the distance L between the platens.

As described above, if the optimum injection compression is started at the point where the shrinkage of the resin is most advanced, the best effects can be obtained on the internal stress, transferability, shape and the like of the molded article. In step S15, the point at which the degree of decrease in the distance L between the platens is largest, that is, the inflection point, is the timing at which the resin shrinks most during the pressure-holding step. Start timing can be found automatically.

Accordingly, in step S15, the distance L between the platens is lowered from this inflection point to increase the mold clamping force to compress the mold opening Δd, thereby increasing the internal pressure in the cavity and increasing the cavity pressure. It acts to equalize (even out) the internal pressure inside. This can prevent the occurrence of local sink marks.

As described above, according to steps S14 and S15, after the distance L between the platens reaches the maximum value, the injection compression is started from the time when the decreasing rate of the distance L between the platens with respect to the time becomes the maximum, and By performing the control of increasing the mold clamping force by lowering the distance L,
Not only can the timing of the increase in the mold clamping force be determined automatically, but also the occurrence of sink marks is reduced most effectively.

In step S16, which is a feature of the present invention,
The microprocessing unit 43 detects the minimum inter-platen distance L _M from the current inter-platen distance.
A first-order lag function pattern L _P2 aimed at up to (overlapping with the area of the mold clamping force P on the drawing) is generated, and the pressure control valve 42 is set so that the distance L between the platens follows this pattern L _P2. Control. Similarly to the above-described function pattern L _P1 , this pattern L _P2 can be set arbitrarily by changing the time constant T ₂ defining the same, and the set value of the time constant T ₂ can be changed. A plurality of fixed values are stored in the memory 44, and the operator sets the solidification speed of the resin,
It may be possible to select an optimum pattern according to the shape of the molded product. 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 injection compression operation of the present invention, the distance between the platens is controlled by a simple setting so as to change in accordance with a smooth descent pattern that the drive source can easily follow. It is possible to more ideally compensate for the shrinkage due to cooling and solidification of the resin. In addition, the time for setting the conditions for non-defective products can be shortened, and the change in the distance between the platens has good reproducibility for each shot.
A stable compression operation can always be realized without being affected by fluctuations in the operating oil temperature or the mold temperature of the hydraulic mechanism.

[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 a change in a mold clamping force and its differential value for explaining the timing of VP switching according to the present invention.

FIG. 9 is a diagram showing an example of a function pattern for defining a distance between platens generated according to the present invention.

FIG. 10 is a diagram for explaining a principle of detecting an inflection point of a change in a distance between platens according to the present invention.

FIG. 11 is a diagram illustrating an example of an injection compression operation based on a distance between platens according to the present invention.

[Explanation of symbols]

 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

Continuation of the front page (56) References JP-A-5-237894 (JP, A) JP-A-54-145757 (JP, A) JP-A-63-145020 (JP, A) JP-A-5-1729 (JP) , B2) Tokuho Hei 4-9652 (JP, B2) (58) Fields surveyed (Int. Cl. ⁶ , DB name) B29C 45/26-45/37 B29C 45/56 B29C 45/64-45/70 B29C 45/76-45/82

Claims (3)

(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. And a drive source for performing the following: a distance sensor for detecting a distance L between the platens of the two platens, a pressure sensor for detecting a tightening pressure by the drive source, and the distance sensor And a control unit that controls the drive source using a distance detection signal of the pressure sensor and a pressure detection signal indicating a mold clamping force from the pressure sensor . Of the resin in
Decrease in the distance L between the platens due to shrinkage due to cooling and solidification
When an inflection point in a small process is detected and the inflection point is detected,
The injection compression molding starts, starting the injection compression molding,
The platen distance L between the arrival point a predetermined value L _M, resin
Wherein the drive source is controlled so as to follow a solidifying speed and a smooth descending pattern according to the shape of the molded product . 2. A control method for an injection molding machine according to claim 1, wherein said control section generates a function pattern whose shape can be arbitrarily changed as said descending pattern. method. 3. The control method for an injection molding machine according to claim 1, wherein said control unit is capable of selecting said descending pattern from a plurality of predetermined patterns. Control system for molding machine.