JP2917089B2 - Control method of injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control system for an injection molding machine, and more particularly to a control system which is effective for preventing the occurrence of defects such as burrs, warpage and sink marks, and which 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 It is important to control the opening amount, that is, the distance between the mold parting surfaces.

As for the control of the mold clamping force, the set value F (ton) of the mold clamping force is generally calculated based on the formula of F = A · P / 1000. The mold clamping force in the injection step and the cooling step including the step and the pressure holding step is set by the operator based on experience and technology.
A is the pressure receiving area of the molded product (cm ² ), and P is the average internal pressure of the mold (kg / cm ² ).

[0004]

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

However, in such a method relying on the experience and technology of the operator, it takes a long time to determine the molding conditions, and in some cases, it is not possible to determine the optimal molding conditions.

[0006] As another method different from the above-mentioned method, there is a method of controlling the injection pressure, the holding pressure, and the mold clamping force so that the mold opening amount is constant during the filling / holding step, and eliminating various defects. .
However, even in the method of controlling the thus set mold opening amount as a target value, when a molded product or a mold changes,
Since the type of resin, the rigidity of the mold, the thickness of the molded product, and the like also change, there is a disadvantage that the setting of the mold opening amount must be changed each time. That is, the operator's experience and skills are required for the profile of the mold opening amount, and time is required to determine the molding conditions as in the above-described method.

Further, the injection pressure is controlled so that the mold opening amount is constant.
The method of controlling the holding pressure has a problem in that the control is difficult 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 method of an injection molding machine which is effective in preventing short shots, welds, burns, and the occurrence of defects such as burrs and sink marks.

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

[0010]

According to the present invention, there is provided a stationary mold attached to a fixed platen, a movable mold attached to a movable platen, and the stationary mold and the movable mold driven by driving the movable platen. In an injection molding machine having a drive source for performing 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. A control unit for controlling the drive source, the control unit performs mold clamping with a minimum mold clamping force necessary to close the mold after mold closing is completed, and resin filling is started. Then, during the filling process, the opening amount is kept at a constant value L _0.
Controlling said drive source so that, then, after following the switching to pressure holding process from the filling step includes a control means controls said drive source so as to maintain the clamping force at the switching point I do.

[0011]

As described above, immediately after completion of the mold closing, resin filling is started in a state where a minimum mold clamping force enough to move the movable platen is applied, and in the filling process, the resin is driven with the mold opening amount as a target value. When the power source is controlled and the charging process is switched to the pressure-holding process, the drive source is controlled using the mold clamping force at the time of the switching as a target value, and in particular, the mold after the switching from the charging process to the pressure-holding process is controlled. The difference between the mold pressure near the gate inside the mold and the mold pressure at the flow end furthest from the gate,
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 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 fixed mold 17 and the movable mold 18 have a mold opening amount sensor for detecting a delicate opening amount between each parting surface 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. FIG. 2 shows the configuration of a control system for that purpose. FIG.
, The detection signal indicating the mold opening L from the mold opening sensor 27 is amplified by the amplifier 30 and the initial mold opening storage device 31
Is input to The initial type opening amount storage device 31 controls the control signal S
_{When a} changes from low level to high level, amplifier 3
Storing the mold opening amount of from 0 to output to the subtracter 32 as an initial type Hirakiryou L _0. The subtracter 32 subtracts the current mold opening L detected by the amplifier 30 from the initial mold opening L _0, and outputs a subtraction result ΔL to the compensator 33. Compensator 33
May be a feedback compensator such as a general PID.
The compensation calculation value F is output to the mold clamping force storage device 34 and the switch 35.

[0016] clamping force storage device 34, the control signal S _b is stored compensation calculation value F from the compensator 33 when the changes from low level to high level, switching unit 35 so as clamping force F ₀ Output. The signal synthesizer 38 controls the control signals S _a , S
The _b as input, outputs a connection switching signal S _c that connect to command as shown in FIG. 4 with respect to switching unit 35 in accordance with a combination of these levels shown in FIG. The switch 35 has a first switch terminal C ₁ for receiving a signal representing a minimum required clamping force set value F ₁ and a second switch terminal C for receiving a signal representing a compensation operation value F from the compensator 33. ₂ and clamping force storage device 3
A third switching terminal C ₃ for receiving a signal indicative of the clamping force F ₀ from 4, and a common terminal C _4, by the connection switching signal S _c from the signal synthesizer 38 and the common terminal C ₄ first To the third switching terminal, and selectively outputs the signal of the connected switching terminal to the amplifier 36.

The signal selected and output by the switch 35 is
Pressure control valve 2 through amplifier 36 as a set value of mold clamping force
9. 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 set value F ₁ given to the _first switching terminal C ₁ are all output from a control device (not shown). 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 running, various operations are performed by a combination of the flow control valve of the drive oil (not shown).

Next, the flowchart shown in 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 switching terminal C ₁ to the common terminal C ₄ .

In step S2, the control section 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,
Minimum clamping force F ₁ of the minimum extent capable of moving the movable platen is provided, unnecessary clamping force is not applied.

[0020] The control signals S _a step S3 is at the high level is stored Early Hirakiryou storage device 31 in the mold fully closed mold opening amount L, initial type Hirakiryou storage device 31 initially a stored value and outputs as the mold opening amount L ₀ until the next molding cycle.
The control signal S _{for a} change to high level, connect switching signal S _c for the switching unit 35 and the second switching terminal C ₂
A signal indicating the connection between the common terminal C ₄ and. As a result, the switch 35 changes the compensation operation value F of the compensator 33 to the amplifier 3
6 and the process proceeds to step S4. At the same time, resin filling is started, and in step S4, the initial mold opening amount L ₀
Null control for maintaining the initial type Hirakiryou L ₀ the mold opening amount by controlling the pressure control valve 29 as a target value 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), this does not mean that the mold opening amount is 0.

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

[0022] switches from the filling process to the pressure holding step, also the control signal S _b in addition to the control signal in step S6 S _a is at a high level, the mold clamping force storage device 34 from the filling process to the pressure-holding step 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 unit 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. The control signal S _b that changes to the high level, the connection switching signal S _c is a signal for specifying the connection between the common terminal C ₄ and the third switching terminal C _3. As a result, the process proceeds to step S7, in which the switching unit 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. Thus, control for the pressure control valve 29 is performed.

In step S8, while the pressure control valve 29 is controlled with the mold clamping force F ₀ as a target value, the process waits for the end of the pressure holding step and the cooling step. Step S when the cooling process is completed
9, and in step S9, the control signals S _a and S _b are both set to low level and the switch 35 is switched to the first switching terminal C.
₁ to end the operation by commanding the connection to the common terminal C _4.

The above-described control method of the present invention and the conventional control method will be compared and studied with reference to FIGS. First, in the conventional control method, a high-pressure mold clamping force is generated before the filling step, and is maintained at a constant mold clamping force during the filling-pressure-holding-cooling step. For this reason, the air or gas trapped in the mold during the filling process is compressed and hinders the filling, and FIG.
As shown in the figure, immediately after switching from the filling process to the pressure-holding process, there is a large difference in the mold inner pressure between the vicinity of the gate of the mold and the flow end farthest from the gate, and this causes the occurrence of defects such as sink marks and warpage. Had become.

On the other hand, in the present invention, at the start of filling, the mold clamping force is sufficiently smaller than the conventional constant mold clamping force, and only the minimum clamping force necessary to keep the mold closed is applied. Air and gas escape easily, and the filling property is improved.
Further, at the time of switching from the filling step to the pressure holding step, the resin is replenished while the mold clamping force is kept constant. Therefore, after switching to the pressure holding step, the mold is opened and the cavity is temporarily enlarged. In the present invention, since the mold is closed with a 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 with a high pressure mold clamping force, and the cavity is temporarily enlarged. Therefore, the flow of the resin is improved even at the flow end farthest from the gate, and the pressure is easily transmitted. In addition, since the cavity is temporarily enlarged near the gate of the mold and serves as a cushion, a surge (peak) pressure is less likely to be generated in the mold internal pressure.

As a result, as shown in FIG. 6 (b), the mold is made uniform so that the difference between the pressures in the mold near the gate of the mold and at the flow end farthest from the gate is small. In addition, since the mold clamping force is automatically maintained when switching from the filling process to the pressure holding process, there is no need for setting by the operator,
Molding can be performed with a minimum mold clamping force without generating burrs.

In the description of the embodiment, the switching timing from the filling step to the pressure-holding step is not described in detail since a known method can be used, but the switching timing is automatically determined by the following method. Can be set manually. That is, the inflow / outflow portion 24-1 is connected to the hydraulic cylinder 24.
A pressure sensor for detecting the pressure on the side is provided, and a differential value ΔP of the mold clamping force P detected by the pressure sensor is monitored. When the differential value ΔP exceeds a predetermined value, switching to the pressure holding step is performed. Do. This is because the mold is about to be opened when the resin is filled in the mold as the filling progresses, and in order to maintain the initial mold opening amount L ₀ , the mold clamping force P is changed as shown in FIG. This is because, as shown in FIG. According to such a determination operation, the filling of the resin in the mold can be accurately detected, and the ideal switching between the filling process and the pressure-holding process can be performed without any special setting such as a conventional timer. It can be carried out. Further, the determination of the switching timing based on the differential value ΔP of the mold clamping force may be performed when the differential value ΔP stops increasing and reaches a constant value.

In FIG. 6B, after switching to the pressure-holding step, the mold clamping force is kept constant until the cooling step is completed. It suffices to perform this operation only for a certain period of time immediately after the switching to.

Further, as shown in FIG. 1, the opening amount between the molds is detected by a mold opening amount sensor provided on the fixed mold and the movable mold. And a sensor for detecting the distance between them may be provided, and the mold thickness including the mold opening amount or the partial mold thickness may be used as the opening amount.

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.

[0031]

According to the present invention, it is possible to omit the setting of the mold clamping force and the setting of the mold opening amount, which have conventionally required the setting by the operator. In addition, the minimum mold clamping force that does not generate burrs can be automatically generated, and there is no need to apply unnecessary force. Therefore, the durability of the mold and the durability of the mold clamping device can be improved. The required minimum mold clamping force is applied during the pressure-holding step, and the mold opening is intentionally increased, whereby the mold internal pressure can be made uniform, and the necessary minimum mold pressure can be obtained. As a result, a molded article free from defects such as sink marks and warpage can be obtained.

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

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

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

FIG. 5 is a flowchart illustrating a control operation according to the present invention.

FIG. 6 shows a mold opening amount in a process of a control operation according to the present invention;
FIG. 4 is a diagram illustrating changes in a mold clamping force, an injection speed / pressure, and a mold inner pressure.

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

[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 Mold opening sensor

Claims (1)

(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 control unit for controlling the drive source using a distance detection signal from the distance sensor for detecting an opening amount L between the two molds. Having the control unit, after the mold closing is completed, performs the mold clamping with the minimum mold clamping force necessary to close the mold, and when the filling of the resin is started, during the filling process, amount of opening the controls the driving source so that a constant value L _0, then after than was switched to the pressure-holding process from the filling process, the drive to maintain the clamping force at the switching point A control method for an injection molding machine, characterized by controlling a source.