JPH07100883A - Control method for injection molding machine - Google Patents

Abstract

PURPOSE:To prevent generation of defects such as flashes, sink marks, warping and the like while releasing air and gas in a mold effectively in the filling process. CONSTITUTION:A distance sensor 28 for sensing the distance L between a fixed platen and a movable platen, a pressure sensor 27 for sensing the clamping pressure to a mold and a microprocessing unit 43 for controlling a driving source by utilizing distance sensing signals from the distance sensor and pressure sensing signals from the pressure sensor are provided in a control method. When the filling of resin is started, a step for controlling the distance between platens to be a constant value LO by the microprocessing unit and retaining the state of contact by the required lowest mold clamping for the purpose of closing the mold is put into practice.

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 having an excellent effect of preventing defects such as burrs, sink marks and warps.

[0002]

2. Description of the Related Art Generally, injection molding of a resin product is carried out by the steps of plasticizing resin, filling, holding pressure, and cooling. In order to obtain a good quality molded product, in addition to controlling the mold temperature consisting of a fixed mold and a movable mold, the resin temperature inside the mold, the injection pressure, etc., it is necessary to set the mold clamping force for the mold. is important.

Regarding the control of the mold clamping force, the set value F (ton) of the mold clamping force is generally calculated based on the formula F = A · P / 1000, and until now, the filling has been performed. The mold clamping force is kept constant in the injection process including the process and the pressure holding process, and the cooling process. A is the pressure receiving area of the molded product (c
m ² ) and P is the average internal pressure of the mold (kg / cm ² ).

[0004]

However, when the mold clamping force is set to a high level in such a control method, it is generated from the air or the molten resin in the mold when the resin is filled in the mold. The generated gas is not discharged from the mold at the end of the injection process and is compressed and remains in the mold, causing defects such as short shots, welds, and burning. In this case, the operator operates to lower the set value of the mold clamping force in order to easily discharge the air and gas in the mold, but if the set value is lowered too much, burrs are likely to occur this time. A problem arises.

Therefore, in the parting surface of the mold, a gap of several μ to several tens of μ, which is called an air vent, is provided, and particularly in the case of molding a thermosetting resin in which gas is easily generated, the metal is immediately filled with the resin. The gas is released by setting the so-called mold opening amount so that the mold is opened only a small amount, or the mold is opened only a minute when the resin has spread to every corner of the molded product just before it is full.

However, even with such a method, since the mold is merely processed or set in order to obtain a gap and a mold opening amount necessary for letting out gas, the burr is completely removed. It is difficult to prevent.

In view of the above-mentioned problems, an object of the present invention is to prevent air and gas in the mold from being efficiently escaped during the filling process, while preventing the occurrence of defects such as burrs, sink marks and warps. It is to provide a control system for an injection molding machine.

[0008]

According to the present invention, a fixed mold attached to a fixed platen, a movable mold attached to a movable platen, and the fixed mold and the movable mold by driving the movable platen. In an injection molding machine having a drive source for opening and closing, and for performing mold clamping, a distance sensor for detecting a platen distance L between the two platens and a clamping pressure by the drive source. It has a pressure sensor and a control unit that controls the drive source using the distance detection signal from the distance sensor and the pressure detection signal from the pressure sensor, and the control unit starts filling the resin. And, during the filling step, controlling the drive source so that the distance between the platens is a constant value L _O, and maintaining the contact state with the minimum mold clamping force required to close the mold. Special to do To.

[0009]

The above control operation takes into consideration that when the resin has spread into the mold, the gas may be trapped because the resin also flows to the outlet for the gas in the mold to escape. It is an action. For this operation, it is effective to allow the gas to escape from the way the resin spreads in the mold, and generally, from about 70 to 80% of the total injection stroke until the resin fills the mold. It is based on the finding that it is better to let the gas escape. By such an operation, air and gas are discharged from the spreading stage before the resin is full in the mold, and the operator must set the minimum mold opening amount required to remove the air and gas. Even if it does, the control unit automatically controls.

[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 of an injection molding machine to which the present invention is applied. In the injection device, the resin charged from the hopper 11 is melted in the heating cylinder 12, measured and kneaded by the screw 13, and the molten resin is stored in front of the screw 13. The stored resin passes 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, and the fixed mold 1
It is filled in the cavity formed by 7 and the movable mold 18. It should be noted that driving oil, whose flow rate or pressure is controlled, flows into and out of the injection cylinder 14 through the inflow / outflow portion 14-1 in accordance with the filling and pressure-holding steps.

On the other hand, the mold clamping device is fixed to a frame (not shown), and the rear platen 22 has four tie bars 23 (2 in the figure) with respect to the fixed platen 21 having the fixed mold 17.
Only the book is shown). A hydraulic piston 25 is arranged in a hydraulic cylinder 24 fixed to the rear platen 22, and a movable platen 26 to which a 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 as the hydraulic piston 25 moves. That is, the movable platen 26 moves in the mold closing direction when injecting the driving oil 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 injecting the driving oil from the inflow / outflow portion 24-2. Moving.

The hydraulic cylinder 24 is provided with a pressure sensor 27 for detecting hydraulic pressure so that the hydraulic pressure in the hydraulic cylinder on the side of the inflow / outflow portion 24-1 can be detected as a mold clamping force with the mold closed. The mold clamping force can be controlled by adjusting the pressure sensor 27 based on the detected value. Further, the fixed platen 21 and the movable platen 26 have a distance L between the platens.
A distance sensor 28 for detecting the distance is provided so that a subtle opening amount between each parting surface of the fixed mold 17 and the movable mold 18 can be measured. The term "distance between platens" as used herein means a distance between the parting surfaces, that is, a mold thickness including a so-called mold opening amount or a partial mold thickness.
The behavior is almost the same as the mold opening behavior.

2 and 3 show examples of a laser type and an eddy current type distance sensor, respectively. The laser type distance sensor shown in FIG. 2 includes a laser head 28-1 for transmitting / receiving laser light 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 platens is sent from 1 to a control unit described later. Such a laser system has a long measurement span and can measure up to the maximum mold opening amount, and the laser head 28-1 and the reflector 28-2 are not the fixed mold 17 and the movable mold 18, respectively, but the fixed platen. 21, because it is installed on the movable platen 26,
The distance sensor need not be adjusted 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 attached to the mount 30 with a variable stroke, the mold is closed when the mold is replaced. It is only necessary to adjust the sensor part 31 so that it is within the measurement span.

In any of the methods, compared with the method of directly mounting the sensor on the mold, the mold does not need to have a special structure for installing the sensor, and the existing mold does not have the structure for mounting the sensor. However, since it can be used as it is, the workability of die replacement is improved and the die cost can be reduced.

FIG. 4 shows the configuration of a control system necessary for executing the control system according to the present invention. This control system emits based on a setting signal from a setter 41 for inputting a platen distance, a mold clamping force, a pressure detection signal from a pressure sensor 27, a platen distance detection signal from a distance sensor 28, and the like. A microprocessing unit 43 for performing sequence processing of the molding machine, function pattern generation, command value output to the pressure control valve 42 for the hydraulic cylinder 24, a memory 44 for storing data such as platen distance, mold clamping force, and the like. Have.

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

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

In step S2, the mold closing operation is performed as is conventionally done, and 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, fixed mold 17 and movable mold 1
8 are the minimum mold clamping force P required to close them.
_I only received _one .

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

In step S4, resin filling is started.
When filling is started, in step S5, the microprocessing unit 43 sets the pressure control valve 42 according to the platen distance L detected by the distance sensor 28 so that the initial platen distance L _O is maintained as a target value. Control and
The mold clamping force P changes according to this. Thus, the mold clamping force P is changed to change the platen distance to the initial platen distance L.
_When filling while maintaining _O , the mold receives only the minimum mold clamping force required to close it, so the air remaining in the mold and the gas generated by the resin are easily discharged, Moreover, since the initial distance L _O between the platens is set as the target value, the parting surfaces of the fixed mold 17 and the movable mold 18 do not open even when receiving the resin filling pressure, and burrs do not occur. By appropriately changing the mold clamping force P according to the filling pressure in this way, 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. It is possible to obtain the effect that the burr can be prevented while facilitating the operation.

In step S6, the microprocessing unit 43 monitors the differential value ΔP of the mold clamping force P detected by the pressure sensor 27, and determines whether or not the differential value ΔP exceeds a predetermined value ΔP ₁ . This is because the mold tries to open due to the progress of the filling and the resin begins to fill in the mold, whereas the microprocessing unit 43, on the other hand, causes the pressure control valve 4 to maintain the initial platen distance L _O.
This is because the command value to 2 is increased to increase the mold clamping force P.

[0023] 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 process. According to such a determination operation, it is possible to accurately detect the filling of the mold with the resin, and further, it is possible to perform ideal VP switching without any special setting such as a conventional timer. .
The determination of the V-P switching timing based on the differential value ΔP of the mold clamping force is, as is apparent from FIG. 8, the differential value ΔP.
May be performed when the increase in the value of the value stops and reaches a certain value. In addition, the reason why the differential value ΔP is used for the determination operation instead of the mold clamping force P itself is that the above determination is difficult because the value of the mold clamping force P changes when the injection condition changes. By using the differential value ΔP, the behavior is always as shown in FIG. 8B regardless of the injection condition, and the above determination is possible.

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 switching in the memory 44 in step S8. Subsequently, in step S9, the microprocessing unit 43 performs the operation of maintaining the mold clamping force P at the target value P ₂ by controlling the pressure control valve 42 with the stored mold clamping force P ₂ as the target value. In this state, the mold is almost filled with the resin, but since the mold is further filled with the resin 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 mitigated. As a result, a so-called cushioning effect can be obtained that prevents adverse effects such as distortion on the molded product.

In step S10, the distance L between platens is increased as the mold is about to open due to the above reason. The microprocessing unit 43 performs an operation of determining whether or not the inter-platen distance L matches the preset start inter-platen distance L _{S at} which the limitation of the inter-platen distance that is set in advance is to be started. If they match, the process proceeds to step S11.

In step S11, the microprocessing unit 43 generates a function pattern L _P having a smooth shape from the limit start platen distance L _S to the predetermined limit end platen distance L _E. Then, the mold control force is adjusted by controlling the pressure control valve 42 so that the platen distance L follows the function pattern L _P with the value defined by the function pattern L _P as the target value.

The function pattern L _P is, for example, a first-order lag function when L _E > L _{S as} shown by the solid line in FIG. 9, and is L _E <L _{S as} shown by the broken line, for example. It is an exponential function. As described above, in step S11, it is possible to limit the maximum inter-platen distance at which burrs do not occur, so that it is possible to prevent burrs from occurring. In addition, since the distance between the platens is controlled while suppressing abrupt changes in resin flow in the mold with a smooth change pattern, the pressure difference between the area near the gate and the area remote from the gate in the mold is reduced. It is possible to prevent the occurrence of defects such as sink marks, warps and the like.

[0028] 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 the optimum conditions according to the thickness of the molded product and the type of resin (viscosity, temperature characteristics, solidification rate, etc.). For example, resin has compressibility, so if the molded product has a large wall thickness,
Since the resin is filled even after the inter-platen distance L reaches the restriction start inter-platen distance L _S , it is possible to adopt a method of gradually opening the mold with L _E > L _S. On the contrary, for a thin wall, since the platen distance L is less filled after reaching the limit start platen distance L _S , L
It is possible to adopt a method of gradually closing the mold with _E <L _S.

It should be noted that ΔL = L _S −L _E and a plurality of kinds of set values of the time constant T ₁ are set as fixed values and stored in the memory 44, and the operator starts the distance L between the limit platens for starting the limit
_The optimum pattern may be selected by setting _S and selecting the optimum value from these values.

In step S12, the microprocessing unit 43 determines whether or not the value defined by the function pattern L _P matches the limit end platen distance L _E, and if the values match, the generation of the function pattern L _P ends. Then, the process proceeds to step S13. In step S 13, the microprocessing unit 43 measures the mold clamping force P ₃ at the end of the generation of the function pattern L _P and stores it 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 gate sealing of the die progresses as the holding pressure progresses, so that the resin is less filled in the die, and in addition, the resin in the die cools and contracts due to solidification, thereby causing a space between the platens. The distance L decreases. in the meantime,
The microprocessing unit 43 monitors the twice differential value d ² L / dt ² of the platen distance L to detect the inflection point of the change in the platen distance L, that is, the minimum value of the differential value ΔL of the platen distance L. And at the time of detection, step S1
The process proceeds to step 6 and the mold clamping force is increased to start injection compression. In addition,
The principle of detecting the inflection point can be determined by the fact that the second differential value d ² L / dt ² of the platen distance L becomes 0, as shown in FIG.

In terms of the optimum injection compression start timing, the purpose of injection compression is to compensate the shrinkage of the resin of the molded product on the mold clamping side. In this case, if the timing of compression is too early, the temperature of the resin will be high, causing backflow from the gate of the mold to the nozzle side, or sinking due to the resin in the mold moving, etc. Can't expect On the other hand, if the timing of compression is too late, solidification proceeds on the surface of the molded product in the mold, and uniform pressure cannot be applied to the entire surface. That is, when the compressive force is low, the compressive force cannot be transmitted to the part where the solidification is not advanced, and when the compressive force is high, the pressure is applied too much to the part where the solidification is advanced, resulting in distortion.

On the other hand, the present inventor has found that the optimum injection compression is most effective for the internal stress, transferability, shape and the like of the molded product when it is started at the point where the shrinkage of the resin is most advanced. . Platen distance L in step S15
The point at which the degree of decrease is largest, that is, the inflection point, is also the timing at which the resin shrinks most during the pressure-holding process. From this, according to the inflection point detection method, the optimum injection compression start timing can be automatically found.

In step S16, the microprocessing unit 43 generates a first-order lag function pattern P _P targeting from the current mold clamping force P ₃ to a preset maximum mold clamping force P _M , and this mold clamping force is generated. The pressure control valve 42 is controlled so as to follow the pattern P _P. This pattern P
Similarly to the above-mentioned function pattern L _P , _P can also be arbitrarily set by changing the time constant T ₂ defining this, and the set value of the time constant T ₂ is fixed. The value may be stored in the memory 44 so that the operator can select the optimum pattern according to the resin solidification speed, the shape of the molded product, and the like. Alternatively, this pattern P _P may be a simpler function, for example, a linear function, depending on the processing capacity of the microprocessing unit 43.

In step S17, the microprocessing unit 43 monitors whether the mold clamping force defined by the function pattern P _P matches the maximum mold clamping force P _M, and if they match, the process proceeds to step S18 to hold the pressure. Complete the process.
This is because when the resin in the mold is cooled and solidified before and after the inflection point in step S15, and the mold clamping force by the function pattern P _P matches the maximum mold clamping force P _M , the mold gate is already in place. This is because there is no need to apply a holding pressure after being sealed. Therefore, this timing can be used as the condition for completing the holding pressure.

Thus, one molding cycle is completed.

Although this example shows a hydraulic molding machine, the present invention can also be applied to a disk molding machine or an electric molding machine. It goes without saying that not only the pressure but also the pressure can be controlled by making the pressure correspond to the current and the torque.

[0038]

As described above, according to the present invention, by controlling the distance between the platens to be constant with the minimum mold clamping force required for closing the mold during the injection process, Since it is possible to effectively discharge the air and gas that are easily trapped in the mold, the burr of the molded product,
It is possible to eliminate defects such as sink marks, warpage, and distortion.
Moreover, since the lowest injection pressure and mold clamping force for obtaining a good product can be realized, energy consumption can be reduced.

[Brief description of drawings]

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

FIG. 2 is a diagram for explaining 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, the mold clamping force, the injection speed and the pressure in the course of the control operation according to the present invention.

FIG. 8 is a diagram showing changes in the mold clamping force and its differential value for explaining the timing of V-P switching according to the present invention.

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

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

[Explanation of symbols]

 11 Hopper 12 Heating Cylinder 13 Screw 14 Injection Cylinder 15 Piston 16 Nozzle 17 Fixed Die 18 Movable Die 21 Fixed Platen 22 Rear Platen 23 Tie Bar 24 Hydraulic Cylinder 25 Hydraulic Piston 26 Movable Platen 27 Pressure Sensor 28 Distance Sensor

Claims (1)

[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 the mold is clamped. In the injection molding machine having a drive source for performing the above, a distance sensor for detecting a platen distance L between the two platens, a pressure sensor for detecting a tightening pressure by the drive source, and the distance sensor Of the distance detection signal and the pressure detection signal from the pressure sensor to control the drive source, the control unit, when the filling of the resin is started, during the filling step, The injection is characterized in that the driving source is controlled so that the distance between the platens becomes a constant value L _O, and the step of maintaining the contact state with the minimum mold clamping force required for closing the mold is executed. Molding machine control method .