JP3588013B2 - Injection molding method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an injection molding method, and particularly to an injection molding method for controlling a booster ram type mold clamping device by a servo valve.
[0002]
[Prior art]
2. Description of the Related Art For example, in molding optical disk molded products such as CDs and DVDs, injection molding has been conventionally performed using a booster-ram type mold clamping device. In the booster ram type clamping device, a small-diameter booster ram 25 is arranged inside a clamping ram 21 as shown in FIG. The fast forward is enabled by the operation of the booster ram 25.
4, reference numeral 11 denotes a fixed plate, 13 denotes a fixed mold, 17 denotes an injection device, 22 denotes a mold clamping cylinder, and 26 denotes a booster cylinder formed on the mold ram 21. Since the configurations of the mold clamping device 20 and the injection device 17 are the same as those of the conventionally known device, the detailed description is omitted.
[0003]
As shown in the control circuit diagram of FIG. 4 and the operation explanatory diagram of FIG. 5, the conventional booster ram type mold clamping device 20 sends pressure oil to the operation circuit 32 of the booster ram 25 when closing the mold. By means of the booster ram 25, the movable die 14 together with the movable die 12 is advanced by rapid feed to the die closing position S of the fixed die 11 with respect to the fixed die 13. When the movable mold 14 advances to the mold closing position S, the pipeline of the hydraulic circuit 31 of the mold clamping device 20 is switched by the switching valve 30, and the mold clamping control of the entire mold clamping ram 21 by the servo valve 40 is performed.
[0004]
The control of the mold clamping ram 21 by the servo valve 40 is sequentially performed by a timer. First, as shown in the column of the clamping pressure of the clamping ram in the operation explanatory diagram of FIG. 5, a fixed time t1 is measured from the mold closing position S, and the low pressure p1 is maintained during this time. Next, after the expiration of the time t1, the voltage is boosted p2 for a predetermined time t2, and after the expiration of the time t2, the high pressure p3 is maintained for a predetermined time t3.
In FIG. 4, a broken line represents the control circuit, reference numeral 41 is a setter, 42 is a pressure detector, 43 is a control device, 44 is a servo amplifier, and 45 is a timer.
[0005]
The relationship with the injection molding machine is as follows. After the hydraulic circuit 31 of the mold clamping device 20 is switched to the pressure control by the servo valve 40, after a predetermined time t4 has elapsed by the delay timer, the injection and filling of the molten resin by the injection device 17 is performed. At this time, the mold clamping force of the movable mold 14 is controlled to the low pressure p1 within the time t1, and the movable mold 14 is slightly retracted by the injection pressure of the injection device 17 to open the mold m. At the timing when the filling of the molten resin material is completed, the mold clamping by the low pressure p1 at t1 is completed, and the pressure rises to p2 for the next fixed time t2, and after the time t2 expires, high pressure control is performed to maintain the pressure p3.
[0006]
As described above, in the conventional mold clamping control, the movable mold 14 is once advanced to the mold closing position S, and the movable mold 14 is slightly retracted (opened) by the pressure at the time of injection filling of the molten resin by the injection device 17. This allows gas to escape during filling and material filling. However, when the mold is opened by the injection pressure of the injection device 17, the resin pressure increases and the pressure loss increases. In addition, the mold opening m at this time cannot be controlled, and since the high pressure is maintained thereafter, residual stress is easily generated in the molded product. For this reason, there is a possibility that a slight warpage may be caused in a thin plate-shaped molded product, and in particular, in an optical disc molded product in which high smoothness is required on the inner and outer peripheries of the plate surface, the improvement of the birefringence is improved. There was a problem that it could not be achieved.
[0007]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and reduces the pressure loss during molding to reduce the residual stress of molded products, eliminates the problem of warpage and distortion of molded products, and particularly applies to optical disc molded products. Another object of the present invention is to propose a novel injection molding method which improves the birefringence and enables high-precision molding.
[0008]
[Means for Solving the Problems]
That is, the present invention relates to an injection start position retracted by a predetermined distance from a mold closing completion position (D) of a movable die in an injection molding machine for molding an optical disk in which a clamping ram and a booster ram of a booster ram type clamping device are controlled by a servo valve. setting the stop position of the mold closing position is (a), the setting defines a mold position a predetermined distance before than the stop position as the gain switching position (B), and set type type closing force of the movable die in the re-mold closing A closing pressure (P), an arbitrary mold closing force from the start of re-mold closing to the set mold closing pressure is determined as a control switching pressure (Pa), and at the time of closing the mold, the movable mold has the gain by the booster ram of the mold clamping device. When moving to the switching position (B), the mold clamping device controls the servo valve by switching the pipeline so as to generate the entire clamping force, and the movable mold is moved to the set stop position (A Is reached, the servo valve performs position control to hold the movable die at the set stop position, and injects molten resin from the injection device while the movable die is held at the set stop position (A). Then, after the screw of the injection device has advanced a predetermined distance from the start of the injection filling or after a predetermined time has elapsed, re-mold closing of the movable mold is started, and the mold closing completion position (D) is set as a movement target value. was carried out, the re-type the rising process of the mold closing pressure in the closed time by detecting the rise of the mold closing pressure type closing pressure of the movable die is the control switching pressure force from the position control when it reaches the (Pa) to the pressure control The present invention relates to an injection molding method characterized in that pressure control for switching and holding the movable mold at the set mold closing pressure (P) is performed by the servo valve.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a control circuit diagram of a mold clamping device showing an embodiment of the present invention, FIG. 6 is a graph comparing the birefringence of an article and a disc molded article molded by a conventional method.
[0010]
The present invention relates to an injection molding method for an injection molding machine in which the booster ram type mold clamping device 20 is controlled by a servo valve 40. In FIG. 1, the same reference numerals as those in FIG. 4 represent the same components, and reference numeral 50 denotes a position detector for detecting the mold position of the movable mold 14. Note that, similarly to FIG. 4, the details of the mold clamping device 20 and the injection device have the same configuration as those of the conventionally known device, and thus description thereof will be omitted.
[0011]
In the method of the present invention , the mold closing position, which is the injection start position retracted a predetermined distance from the movable mold closing completion position (D) of the movable mold, is set as the set stop position A, and is set a predetermined distance before the set stop position A. Is determined as the gain switching position B. Further, the movable mold closing force at the time of re-mold closing is defined as a set mold closing pressure P, and an arbitrary mold closing force from the start of re-mold closing to the set mold closing pressure is defined as a control switching pressure Pa. The set stop position A is the mold position of the movable mold 14 at the time of starting the injection, and the movable mold 14 is slightly retracted by the injection filling pressure by the injection device 17 from the mold closed position S in the conventional method, and the mold opening m This is equivalent to the position that has been set, and is determined empirically. The gain switching position B is a switching position of the output gain, as described later. The gain switching position B controls the pressure oil line so that the servo valve 40 controls the position and the pressure of the movable die 14 by the full clamping force of the clamping device. This is the switching position. The set mold closing pressure P is a pressure for so-called high-pressure mold clamping after injection and filling of the molten resin. The control switching pressure Pa can be any mold closing force from the start of re-mold closing to the set mold closing pressure P.
[0012]
According to the present invention, the position of the booster ram type mold clamping device 20 is controlled by the servo valve 40 to the set stop position A with respect to the movable die 14 at the time of starting the injection, and the set relative to the movable die 14 at the time of re-mold closing. The pressure is controlled to the mold closing pressure P.
For this reason, when closing the mold, when the movable mold 14 is moved by the booster ram 25 to the gain switching position B a predetermined distance before the set stop position A, the pipe of the hydraulic circuit 31 is so generated as to generate the full mold clamping force. The path is switched to control the servo valve 40. That is, the booster ram 25 and the mold clamping ram 21 have different cylinder areas, and the control results are different when the output of the servo valve 40 is the same. Therefore, the output gain is switched by the switching valve 30 to perform appropriate and optimal control. To do it.
[0013]
At the time of closing the mold, similarly to the above, pressurized oil is supplied to the operation circuit 32 of the booster ram 25 and the movable mold 14 attached to the movable plate 12 by the booster ram 25 is moved to the fixed mold 13 of the fixed plate 11. Move forward by fast forward. Then, when the mold position of the movable mold 14 reaches the gain switching position B, as shown in the uppermost column of FIG. 2, the switching valve 30 of the hydraulic circuit 31 is turned on and the output gain is switched. The position detection of the gain switching position B is performed by the position detector 50 shown in FIG.
[0014]
Next, when the movable mold 14 reaches a predetermined set stop position A, the servo valve 40 controls the servo valve 40 to hold the movable mold 14 at the predetermined stop position A based on a signal from the position detector 50. . This set stop position A is an injection start position that is slightly retracted and the mold is opened for injection filling of the molten resin material, which is set back from the movable mold closing completion position (D) by a predetermined distance. May affect molded products. Therefore, it is desirable to use a high-precision position detector (with a resolution of 0.01 mm or less) so that this positional variation can be made to be 0.01 mm or less. In the embodiment, the positioning control is performed by feeding back the mold position in all steps from the mold closing start to the setting stop position A. The servo valve 40 is a four-way valve type so that a delicate mold opening / closing operation can be performed.
[0015]
As shown in the operation explanatory diagram of FIG. 2, after a predetermined time t has elapsed since the movable mold 14 reached the set stop position A, the molten resin was injected from the injection device 17 while the movable mold 14 was held at the set stop position A. Is injection-filled. The reason why the injection is started after a predetermined time t has elapsed since the movable mold 14 has reached the set stop position A is to ensure the stability of holding the mold position of the movable mold 14. When the mold position of the movable mold 14 is out of the allowable range of the set stop position A plus or minus α, an alarm is issued.
[0016]
During injection filling of the molten resin, the movable mold 14 stops at the set stop position A, and holds the set stop position A so as to hold the set stop position A until the next signal to re-close the mold is issued. And the servo valve 40 performs feedback control. In particular, at the start of injection, as shown in the explanatory diagram of FIG. 2, a high injection pressure is applied and a force is exerted to change (retreat) the mold position of the movable mold 14, but it does not shift from the set stop position A. Is controlled. In such a case, the clamping pressure instantaneously increases to maintain the set stop position A as shown in the column of the clamping pressure of the clamping ram in FIG. By the way, in this position control, since the entire clamping force is applied to the clamping ram 21 by switching the pipeline of the pressure oil, the position control can be effectively performed with respect to the injection pressure.
[0017]
After completion of the injection filling of the molten resin, that is, after the screw of the injection device 17 has advanced a predetermined distance from the start of the injection filling or a predetermined time has elapsed, the movable mold 14 is re-closed. The signal of the mold re-closing is performed when a predetermined time elapses from the detection of the advance position of the screw in the injection device 17 or the start of the injection filling by the timer. In the embodiment, as shown in the explanatory diagram of FIG. 2, re-mold closing is started when the time ta of the injection filling timer elapses.
[0018]
Re-mold closing is performed by position control using a mold closing completion position D or a separately set predetermined mold position (not shown) from the re-mold closing start position to the mold closing completion position D as a movement target value. In the embodiment, position control is performed with the mold closing completion position D as a target value. Incidentally, the position control of the movable die 14 of the embodiment is performed with the target of the set stop position A initially, and after reaching the set stop position A, the target of the mold closing completion position D is newly set.
[0019]
At this stage of the mold closing, the mold closing pressure of the movable mold 14 increases. Then, in the present invention, when the mold closing pressure is detected to rise in the course of the rise, and when the control switching pressure Pa set as an arbitrary mold closing force from the start of the re-mold closing to the set mold closing pressure P is reached. Then, the pressure control is switched from the position control to the pressure control, and the movable mold 14 is controlled to the set mold closing pressure P by the servo valve 40. As shown in the explanatory diagram of FIG. 2, when a predetermined control switching pressure Pa is reached, the servo valve 40 is switched to pressure control, and thereafter control for maintaining the set-type closing pressure P is performed.
After the holding control of the set mold closing pressure P of the mold clamping ram 21 is performed by the servo valve 40, the mold is cooled, the molding is completed, and the molded product is taken out.
[0020]
【The invention's effect】
According to the injection molding method of the present invention, since the position of the mold is set to the preset stop position A which is previously opened at the time of starting the injection and the molten resin is injected by controlling the position without changing the position, the molten resin to be filled is Good gas escape, wide gate and cavity flow paths, injection with low resin pressure, reduced pressure loss during molding, and at the same time, reduced pressure during filling, The residual stress can be reduced. Further, since position control for holding the set stop position A is performed at the time of injection filling, there is no change in the mold position, and when the mold is closed again after filling, the pressure is controlled by the set mold closing pressure P. Warpage and distortion in a molded product can be greatly improved, and high-precision molding can be performed on a thin plate-shaped molded product such as an optical disc molded product.
[0021]
The graph of FIG. 3 shows the birefringence index of the optical disc molded product (CD) in comparison with the present invention and the conventional product. As shown by the solid line in the figure, in the present invention, the birefringence is measured from the inner side. A molded product with less distortion on the outer peripheral side is obtained on average. The broken line in the figure is a molded product according to the conventional method, and it can be seen that the birefringence on the inner peripheral side and the outer peripheral side of the disk molded product is greatly improved. In the drawing, both the solid line and the broken line are represented by three lines, but all of them show the experimental maximum value, the average value, and the minimum value.
[Brief description of the drawings]
FIG. 1 is a control circuit diagram of a booster ram type mold clamping device showing one embodiment of the present invention.
FIG. 2 is an operation explanatory view of the mold clamping device of FIG. 1;
FIG. 3 is a graph comparing the birefringence of a disk molded product molded according to the present invention with a disk molded product molded by a conventional method.
FIG. 4 is a control circuit diagram of a conventional booster ram type mold clamping device.
FIG. 5 is an operation explanatory view of the conventional mold clamping device of FIG. 4;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Fixed board 12 Movable board 14 Movable mold 17 Injection device 20 Booster ram type mold clamping device 21 Mold clamping ram 25 Booster ram 30 Switching valve 40 Servo valve 41 Setting device 42 Pressure detector 43 Control device 44 Servo amplifier 45 Timer 50 Position detector

Claims (1)

In an injection molding machine for molding an optical disc in which a clamping ram and a booster ram of a booster ram type clamping device are controlled by a servo valve,
The mold closing position, which is the injection start position retracted by a predetermined distance from the movable mold closing completion position (D), is the set stop position (A), and the mold position a predetermined distance before the set stop position is the gain switching position (B). The movable mold closing force at the time of re-mold closing is defined as a set mold closing pressure (P), and any mold closing force from the start of re-mold closing to the set mold closing pressure is defined as a control switching pressure (Pa). ,
When closing the mold, the servo valve is controlled by switching the pipeline so that the mold clamping device generates a full clamping force when the movable mold is moved to the gain switching position (B) by the booster ram of the mold clamping device. Along with
When the movable mold reaches the set stop position (A), the servo valve performs position control for holding the movable mold at the set stop position,
Injecting and filling a molten resin from an injection device while the movable mold is held at the set stop position (A),
After the screw of the injection device has advanced a predetermined distance from the start of the injection filling or after a predetermined time has elapsed, re-closing of the movable mold is started, and position control is performed with the mold closing completion position (D) as a movement target value. ,
The switched to pressure control from position control when the reached increase the detected mold closing pressure of the movable mold by said control switching pressure force of the mold closing pressure in the rising process of the mold closing pressure during re-mold closing (Pa) An injection molding method, wherein a pressure control for maintaining the movable mold at the set mold closing pressure (P) by a servo valve is performed.

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