JPH07100893A - Control method for injection molding machine - Google Patents

Abstract

PURPOSE:To prevent the generation of defects such as sink marks by so controlling a drive source as to retain the mold clamping force applied at changeover point right after the changeover from the filling process to the dwelling process. CONSTITUTION:A sensing signal representing the mold opening amount L from a mold opening sensor 27 is amplified by an amplifier 30 and inputted into an initial mold opening amount storage device 31. The mold opening amount from the amplifier 30 is stored by the initial mold opening amount storage device 31 when a control signal Sa is varied from the low level to the high level, which is output into a subtracting machine 32 as the initial mold opening amount Lo. A signal selectively output by a changeover machine 35 is supplied as a set value of the mold clamping force to a pressure control valve 29 through an amplifier 36. The hydraulic pressure of a hydraulic cylinder 24 is controlled based on the set value of the input mold clamping force by the pressure control valve 29. When the filling process is changed over to the dwelling process, a control signal Sb is changed over to the high level in addition to the control signal Sa, and a computed compensation value F of a compensator 33 at the changeover point from the filling process to the dwelling process is stored as existing mold clamping force in a mold clamping force storage device 34.

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 which is effective in preventing defects such as burrs, warps and sink marks and which can improve the operability of an operator.

[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 temperature of the mold consisting of a fixed mold and a movable mold, the resin temperature inside the mold, the injection pressure, etc., the mold clamping force against the mold and the mold It is important to control the opening amount, that is, the distance between the mold parting surfaces.

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 in the injection process including the process and the pressure-holding process and the cooling process is set by the operator based on experience and technology.
In addition, A is the pressure receiving area (cm ² ) of the molded product, and P is the average internal pressure (kg / cm ² ) of the mold.

[0004]

When molding is performed by setting the mold clamping force by such a method, when the resin is filled in the mold, the gas remaining from the air or the molten resin remaining in the mold is generated. Is compressed at the end of the filling process, and causes defects such as short shots, welds, and burns in the molded product.
In this case, the operator can gradually reduce the setting of the mold clamping force to the extent that burr does not occur, and eliminate defects such as short shots, welds, and burns.

However, with such a method that relies on the experience and technology of the operator, it takes a long time to find the molding conditions, and in some cases it is not possible to obtain the optimum molding conditions.

As a method different from the above-mentioned method, there is a method of eliminating various defects by controlling the injection pressure, the holding pressure and the mold clamping force so that the mold opening amount becomes constant during the filling / pressure holding process. .
However, even in the method of controlling the mold opening amount set in this way as the target value, when the molded product or the mold is changed,
Since the type of resin, the rigidity of the mold, the wall thickness of the molded product, etc. also change, there is the drawback that the mold opening amount must be changed each time. That is, the experience and skill of the operator are also required for the profile of the mold opening amount, and like the above method, it takes time to find the molding conditions.

Also, the injection pressure is adjusted so that the mold opening amount becomes constant.
In the method of controlling the holding pressure, there is a problem in that this method is difficult to control because a pressure delay occurs from the hydraulic pressure of the injection cylinder to the resin pressure in the mold.

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

Another object of the present invention is to provide a control system for an injection molding machine which can minimize the work of determining and inputting various set values, which has been performed based on the experience and skill of the operator. It is in.

[0010]

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 a mold clamping, a distance sensor for detecting an opening amount L between the two molds and a distance detection signal from the distance sensor are used. And a control unit for controlling the drive source, the control unit performs mold clamping with a minimum mold clamping force required to close the mold after the mold closing is completed, and resin filling is started. Then, during the filling process, the opening amount is a constant value L _0.
The drive source is controlled so as to satisfy the above condition, and immediately after the switching from the filling step to the pressure holding step, the drive source is controlled so as to maintain the mold clamping force at the time of this switching.

[0011]

As described above, immediately after the mold is closed, the resin filling is started with the minimum mold clamping force that allows the movable platen to be moved, and the mold opening amount is set as the target value in the filling process. When the pressure is controlled to switch from the filling process to the pressure-holding process, the mold source at the time of this switching is used as a target value to control the drive source. The difference between the mold internal pressure near the gate inside and the mold internal pressure at the flow end farthest from the gate is reduced,
The pressure distribution in the mold can be made uniform.

[0012]

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 has a rear platen 22 having 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 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 fixed mold 17 and the movable mold 18 have a mold opening amount sensor for detecting a delicate opening amount between the parting surfaces of the fixed mold 17 and the movable mold 18, that is, a mold opening amount L. 27 are provided.

The present invention is particularly characterized in the control of the mold clamping device, and the configuration of the control system therefor is shown in FIG. Figure 2
In, the detection signal indicating the mold opening amount L from the mold opening amount sensor 27 is amplified by the amplifier 30, and the initial mold opening storage device 31.
Entered in. The initial mold opening storage device 31 uses the control signal S
amplifier 3 _{when a} is changed from low level to high level
The die opening amount from 0 is stored, and this is output to the subtractor 32 as the initial die opening amount L ₀ . The subtractor 32 subtracts the current mold opening amount L detected by the amplifier 30 from the initial mold opening amount L _0, and outputs the subtraction result ΔL to the compensator 33. Compensator 33
Is a feedback compensator such as a general PID,
The value F calculated by compensation is output to the mold clamping force storage device 34 and the switch 35.

The mold clamping force storage device 34 stores the compensation calculation value F from the compensator 33 when the control signal S _b changes from the low level to the high level, and stores it in the switch 35 as the mold clamping force F _0. Output. The signal synthesizer 38 controls the control signals S _a and S.
_{Using b} as an input, a connection switching signal S _c for instructing the switching device 35 to connect as shown in FIG. 4 is output according to the combination of these levels shown in FIG. The switching device 35 has a first switching terminal C ₁ for receiving a signal indicating a necessary minimum mold clamping force setting value F ₁ and a second switching terminal C ₁ for receiving a signal indicating a compensation calculation value F from the compensator 33. ₂ and mold clamping force memory 3
4 has a third switching terminal C ₃ for receiving a signal indicating the mold clamping force F ₀ from 4 and a common terminal C _4, and the connection terminal switching signal S _c from the signal synthesizer 38 causes the common terminal C ₄ to be connected to the first terminal. ~ Any one of the third switching terminals is selectively connected to output the signal of the connected switching terminal to the amplifier 36.

The signal selectively output by the switch 35 is
The pressure control valve 2 is passed through the amplifier 36 as the set value of the mold clamping force.
9 is supplied. The pressure control valve 29 controls the hydraulic pressure of the hydraulic cylinder 24 based on the input set value of the mold clamping force.
The control signals S _a and S _b and the mold clamping force setting value F ₁ given to the _first switching terminal C ₁ are all output from a control device (not shown), and this control device works together with the control system shown in FIG. It functions as the control unit of the present invention. Further, the mold clamping force setting value F ₁ is given when the control operation according to the present invention is not executed, and various operations are performed by combination with a drive oil flow rate control valve (not shown).

Next, the flowchart shown in FIG. 5 and FIG.
The control operation of the present invention will be described with reference to FIG. In step S1, the control unit performs a mold closing operation before starting molding. At this time, the control signals S _a and S _b are both at the low level, and as a result, the switch 35 connects the first switch terminal C ₁ and the common terminal C ₄ .

In step S2, the controller determines whether or not the mold is fully closed based on a signal from the mold opening sensor 27. When the mold is fully closed, the process proceeds to step S3. In this state, the fixed mold and the movable mold are in close contact with each other,
The minimum required minimum mold clamping force F ₁ that can move the movable platen is given, and unnecessary mold clamping force is not applied.

In step S3, the control signal S _a is set to a high level to store the mold opening amount L at the time of fully closing the mold in the initial mold opening amount storage device 31, and the initial mold opening amount storage device 31 initializes the stored value. The mold opening amount L ₀ is output until the next molding cycle.
Further, since the control signal S _a changes to the high level, the connection switching signal S _c for the switching device 35 is the second switching terminal C ₂
And a signal for instructing the connection between the common terminal C ₄ and the common terminal C ₄ . As a result, the switching device 35 outputs the compensation calculation value F of the compensator 33 to the amplifier 3
6, and the process proceeds to step S4. At the same time, the resin filling is started, and in step S4, the initial mold opening amount L ₀
By controlling the pressure control valve 29 with a target value of ₀ , the zero control for maintaining the mold opening amount at the initial mold opening amount L ₀ is performed. In this zero control, the mold opening amount when the mold is fully closed in step S2 is regarded as zero.
As is clear from (a), it does not mean that the mold opening amount is zero.

In step S5, the switching from the filling process to the pressure holding process is monitored, and when the switching to the pressure holding process is performed, the process proceeds to step S6. In the filling process,
Since the resin gradually spreads in the mold, the internal pressure to open the mold increases. On the other hand, since the mold opening amount is controlled so as to be maintained at the initial mold opening amount L ₀ before the start of filling, the mold clamping force increases from the latter half of the filling process as shown in FIG. 6B. Go on.

When the filling process is switched to the pressure-holding process, the control signal S _a as well as the control signal S _b is set to a high level in step S6, and the mold clamping force storage device 34 stores the pressure-holding process from the filling process. The compensation calculation value F of the compensator 33 at the time of switching is stored as the current mold clamping force. The mold clamping force storage device 34 outputs the stored compensation calculation value F as the mold clamping force F ₀ at the time of switching from the filling process to the pressure holding process until the next molding cycle. Further, since the control signal S _b changes to the high level, the connection switching signal S _c becomes a signal designating the connection between the _third switching terminal C ₃ and the common terminal C ₄ . As a result, in step S7, the switching device 35 switches to output the mold clamping force F ₀ instead of the compensation calculation value F, and thereafter maintains the mold clamping force F ₀ as the target value. The pressure control valve 29 is controlled so that

In step S8, the pressure control valve 29 is controlled with the mold clamping force F ₀ as a target value, and the process waits until the pressure holding step and the cooling step are completed. When the cooling process is completed, step S
9, the control signals S _a and S _b are both set to low level in step S9, and the first switching terminal C is supplied to the switching device 35.
_The operation is ended by commanding the connection between ₁ and the common terminal C ₄ .

The control method of the present invention described above and the conventional control method will be compared and examined with reference to FIGS. 6 and 7. First, in the conventional control method, a high mold clamping force is generated before the filling process, and the mold clamping force is kept constant during the filling-holding-cooling process. Therefore, air and gas trapped in the mold during the filling process are compressed and hinder the filling, as shown in FIG.
Immediately after switching from the filling process to the pressure-holding process, there is a large difference in the mold pressure between the mold gate and the flow end farthest from the gate, which is the cause of defects such as sink marks and warpage. Was becoming.

On the other hand, in the present invention, at the start of filling, the force is sufficiently smaller than the conventional constant mold clamping force, and only the minimum mold clamping force required to keep the mold closed is applied. Air and gas escape easily, and the filling property improves.
Further, when the filling process is switched to the pressure holding process, the resin is replenished while the mold clamping force is kept constant, so that the mold opens after the pressure holding process is switched and the cavity is temporarily enlarged. Further, in the present invention, since the mold is closed by the low pressure mold clamping force from the beginning, the resin is less likely to be solidified during the flow than when the mold is closed by the high pressure mold clamping force, and the cavity is temporarily expanded. Therefore, even at the flow end farthest from the gate, the resin flow is improved and pressure is easily transmitted. In addition, since the cavity temporarily expands in the vicinity of the gate of the mold, it functions as a cushion, so that surge (peak) pressure is less likely to occur in the mold internal pressure.

As a result, as shown in FIG. 6 (b), the difference in the mold internal pressure between the vicinity of the gate of the mold and the flow end farthest from the gate is made uniform. In addition, the mold clamping force does not need to be set by the operator because the mold clamping force when switching from the filling process to the pressure holding process is automatically maintained.
Molding can be performed with a minimum mold clamping force that does not cause burrs.

In the description of the embodiment, a known method can be used for the switching timing from the filling step to the pressure holding step, so a detailed description thereof is omitted. However, the switching timing is automatically changed by the following method. Can be set as desired. That is, the hydraulic cylinder 24 has an inflow / outflow portion 24-1.
A pressure sensor for detecting the side pressure is provided, the differential value ΔP of the mold clamping force P detected by this pressure sensor is monitored, and when the differential value ΔP exceeds a predetermined value, switching to the pressure holding process is performed. To do. This is because the mold tries to open due to the progress of the filling and the resin begins to fill the mold, and the mold clamping force P for maintaining the initial mold opening amount L ₀ is as shown in FIG. This is because it is controlled to increase as shown in (). According to such a determination operation, it is possible to accurately detect the filling of the resin into the mold, and to switch between the ideal filling process and the pressure-holding process without any special settings such as the conventional timer. It can be carried out. The determination of the switching timing based on the differential value ΔP of the mold clamping force may be made based on the fact that the differential value ΔP stops increasing and reaches a constant value.

In FIG. 6 (b), the mold clamping force is kept constant until the cooling process is completed after switching to the pressure maintaining process, but the control for keeping the mold clamping force constant is performed in the pressure maintaining process. It suffices to do this for a certain period of time immediately after switching to.

Further, as shown in FIG. 1, the opening amount between the molds is detected by a mold opening sensor provided in the fixed mold and the movable mold. It is also possible to provide a sensor for detecting the distance between them and use the mold thickness including the mold opening amount or the partial mold thickness as the opening amount.

Although this example shows a hydraulic molding machine, the present invention can be applied to a disk molding machine and 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.

[0031]

According to the present invention, it is possible to omit the setting of the mold clamping force and the mold opening amount, which have conventionally been required to be set by the operator. Further, since the minimum mold clamping force that does not cause burrs can be automatically generated and unnecessary force need not be applied, it is possible to improve the durability of the mold and the durability of the mold clamping device. By applying the minimum required mold clamping force during the pressure-holding process and intentionally increasing the mold opening amount, the mold internal pressure can be made uniform, and the minimum necessary mold internal pressure can be obtained. As a result, it is possible to obtain a molded product without defects such as sink marks and warpage.

[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 block diagram showing a schematic configuration of a control system according to the present invention.

FIG. 3 is a diagram for explaining the relationship between the waveform of a control signal applied to the control system shown in FIG. 2 and the switching timing of a switch.

FIG. 4 is a diagram for explaining a relationship between a control signal given to the control system shown in FIG. 2 and a connection operation in a switch.

FIG. 5 is a flow chart diagram for explaining a control operation according to the present invention.

FIG. 6 is a mold opening amount in the process of control operation according to the present invention,
FIG. 6 is a diagram showing changes in mold clamping force, injection speed / pressure, and mold internal pressure.

FIG. 7 is a diagram showing changes in a mold opening amount, a mold clamping force, an injection speed / pressure, and a mold internal pressure in the process of a conventional control operation.

[Explanation 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 Mold Opening 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 an injection molding machine having a drive source for performing the above, a controller for controlling the drive source using a distance sensor for detecting an opening amount L between the two molds and a distance detection signal from the distance sensor. And the control section performs mold clamping with the minimum mold clamping force required to close the mold after the mold closing is completed, and when the resin filling is started, during the filling process, The drive source is controlled so that the opening amount becomes a constant value L _0, and immediately after the filling process is switched to the pressure holding process, the drive source is controlled so as to maintain the mold clamping force at the time of this switching. A method of controlling an injection molding machine characterized by: