JP3279118B2 - Injection compression molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection compression molding method, and more particularly to an injection compression molding method for improving the operability and supplying a high-quality molded product continuously and stably.

[0002]

2. Description of the Related Art Conventionally, when performing injection compression molding using an injection molding apparatus that performs mold clamping by a toggle mechanism, (1) the toggle is stopped at an intermediate position during the mold clamping operation to inject molten resin. After that, the toggle was driven again to perform compression. In this case, the toggle is not in a linear state, but in a state of large refraction. (2) The toggle has completed the mold clamping in a straight line state, and in this state, a predetermined gap is secured in the mold. After the molten resin is injected and filled, a compression plate separately attached to a movable platen or a fixed platen is used. The compression was performed by a hydraulic cylinder or the like.

[0003]

However, the above-described method has the following problems. That is,
With respect to (1), since the boosting factor of the toggle mechanism is small, the movable platen is largely retracted due to the injection filling pressure of the molten resin, and a predetermined mold clearance cannot be maintained. Occurs and molding becomes impossible. In order to prevent the above problems, it is necessary to increase the size and complexity of the mold clamping cylinder and to remodel a special hydraulic control valve, etc., resulting in an increase in the complexity and size of the molding machine and an increase in cost. In contrast to (2), a hydraulic cylinder for compression or the like is required separately from the toggle mechanism, which leads to an increase in complexity and cost of the molding machine. The problems common to both (1) and (2) are that it is extremely difficult to set the timing and speed for re-clamping (driving the toggle and driving the hydraulic cylinder). Both require complexity and sophistication. Depending on the setting of the re-clamping timing, it is necessary to drive the injection side and the mold-clamping side at the same time, and an increase in cost is inevitable due to the size and complexity of the drive system. In any case, injection compression molding is impossible without any modification to the existing toggle mold clamping injection molding apparatus.

[0004]

[Means for Solving the Problems] By solving the above problems,
In order to perform high-precision injection compression molding without any special modification to the existing toggle mold injection molding apparatus, the present invention employs an injection molding apparatus having a toggle mechanism equipped with a toggle mechanism. In the molding apparatus, the injection pressure control is performed at an injection pressure capable of filling a mold with a resin amount obtained by adding a cooling solidification shrinkage amount calculated in advance during an injection filling step, and the toggle of the mold clamping apparatus is in a maximum extended state. A mold clamping force that allows the mold to open by extending the tie bar to the mold opening amount corresponding to the cooling, solidification, and shrinkage amount by the resin pressure filled in the cavity of the mold is applied to the mold in advance. In the compression step after the injection filling is completed, the mold is closed by the elastic recovery force of the tie bar.

[0005]

In the injection filling step, the filling is controlled so that the filling can be performed at a high speed in the early stage of filling because the flow resistance of the resin in the mold cavity is small, and the flow resistance of the resin becomes large in the latter stage of the filling. Since the speed is naturally reduced, the ideal natural filling flow (natural / natural) that automatically has a continuous speed gradient during resin filling and does not generate pack pressure
Flow). In addition, by filling the amount of resin plus the amount of cooling solidification shrinkage, and by extending the tie bar with the toggle most extended, the mold clamping force that allows the mold opening amount corresponding to the amount of cooling solidification shrinkage is increased. Since the movable platen does not recede at all due to the injection filling pressure by applying the load, and the resin is almost fully filled (just pack) even when the injection filling is completed, the resin flow rate in the mold is reduced. It is completely unaffected by the occurrence of defects such as flow marks caused by discontinuities. Even during the injection filling and when the compression process is switched, an appropriate mold clamping force is applied to the mold, so that even if the molding conditions fluctuate during the molding, the mold clamping force, that is, the stretching behavior of the tie bar is not affected by the spring. It has the flexibility to work as an elastic action. In the compression process, the mold is closed by the elastic recovery force of the tie bar, so that no unnecessary clamping force is applied to the resin.The compression action corresponds to the cooling, solidification and shrinkage behavior of the resin. Can be extremely small.

[0006]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1 to 4 relate to an embodiment of the present invention, FIG. 1 is an overall side view of an injection molding apparatus, FIG. 2 is an explanatory view showing a correlation between a set mold clamping force and a tie bar elongation amount, and FIG. FIG. 4 is an explanatory diagram showing a correlation between the mold opening amount and a set mold clamping pressure, and FIG. 4 is an explanatory diagram of a process of injection compression molding.

FIG. 1 shows an injection molding apparatus 100 provided with a toggle-type mold clamping device 50. The upper half of the center line shows the maximum extension state of the toggle mechanism 6, and the lower half of the center line shows the tie bars after the completion of injection filling. 12 shows a state in which the movable platen 3 has retreated by the distance S due to the extension of No. 12. Mold clamping device 5 in the figure
0 is a link housing 1, a fixed platen (fixed platen)
2, movable platen (movable platen) 3, mold 4 (fixed mold 4a)
And a movable mold 4b), a toggle mechanism 6, a crosshead 7, a mold clamping cylinder (die lock cylinder) 8, a piston rod 9 and a guide rod 10. Injection molding apparatus 100 having double toggle type mold clamping device 50
Then, as shown in the figure, the movable platen 3 and the link housing 1
A pair of upper and lower toggle mechanisms 6 including three toggle links 6a, 6b, 6c are provided between them, and a mold clamping cylinder (die-lock cylinder) 8 is mounted substantially at the center of the outer end surface of the link housing 1, and mold clamping is performed. The tip of the piston rod 9 of the cylinder 8 is connected to the crosshead 7, the crosshead 7 is moved forward and backward along the guide rod 10 movably inserted and retracted, and the toggle mechanism 6 is operated via the crosshead 7. Then, the movable platen (movable platen) 3 is moved with respect to the fixed platen 2 to perform a mold clamping operation.

In such an injection molding apparatus 100,
First, a resin volume obtained by adding a cooling solidification shrinkage amount of a resin calculated according to resin physical properties to a cavity volume defined by the fixed mold 4a and the movable mold 4b is set as a measurement value,
An injection pressure condition with the best injection efficiency is set as an injection pressure value from an injection filling pressure range in which the cavity 5 can be filled and burrs do not occur. At the same time, the tie bar 12 is extended by the injection-filling behavior from the set measurement value and injection pressure value, the cavity 5 volume and the cavity projected area to the mold opening amount corresponding to the amount of cooling, solidification, and shrinkage of the resin at the time of the completion of the injection filling, thereby being movable. A mold clamping force value that allows the mold 4b to separate from the fixed mold 4a is set. In this case, the die height adjustment (the movable platen, the toggle mechanism, and the housing are integrated by a hydraulic and electric drive device integrated in the housing so that the toggle is in the most extended state.
A method in which the maximum generated mold clamping force is set according to the mold size by adjusting the advance and retreat of the fixed platen. This is a general adjustment method for a toggle mold clamping device. ), The details of which will be described below with reference to FIG.

FIG. 2 shows the relationship between the set clamping force and the tie bar elongation in the toggle mold clamping device. That is, the principle of generation of the mold clamping force in the toggle mold clamping device is that the toggle mechanism 6 is driven to move the movable platen 3 forward, and the movable mold 4b and the fixed mold 4a are touched (at this time, the toggle 6 Since the tie bar 12 is stretched by further pressing the movable platen 3 toward the fixed platen 2, a mold clamping force is generated. Then, in a state where the toggle 6 is stretched most, the mold clamping force shows a maximum value (when the die height is adjusted to a design allowable maximum value) Kmax.
Is extended to the maximum value (△ lmax value).
When injection compression molding is performed using the behavior of the tie bar 12 extending, the maximum allowable elongation of the tie bar 12 (△ lm
ax value) is the adjustable range of the mold opening amount by the injection filling pressure. Usually, a mold clamping force corresponding to the projected area of the cavity is variously set by die height adjustment in order to protect the mold according to the size of the mold attached to the injection molding apparatus. Assuming that the set mold clamping force at this time is, for example, a K ₀ value (the toggle is in a linear state).
Elongation amount of the tie bar 12 (mold opening amount adjustment range) is △ l ₀ value, when the mold opening amount corresponding to the cooling and solidification shrinkage of the resin during the injection completion and S value, the clamping force K previously set by setting at the die height adjusted to smaller clamping force K ₁ values than ₀ value, it is possible to ensure the mold opening amount S value. Note that, even in this state, since the toggle 6 is in the most extended state (linear state), the movable platen 3 does not retreat due to the injection filling pressure.

Further, a state in which the molten resin is almost completely filled at the time of completion of the injection filling (just pack) is defined as an appropriate mold clamping force value. This state will be described in detail with reference to FIG.
FIG. 4 shows the fixed mold 4 when the mold clamping pressure value is changed when the injection filling is performed under the condition that the measured value and the injection pressure value are constant.
The relationship between the distance a from the movable mold 4b and the mold opening is shown. FIG. 3 is a graph of the data obtained in FIG. 3 or obtained by experiments, and the following findings were obtained from this data. That is, in the case of, 250L
A box of × 300W × 50H × 2t (projection area: 750 cm ² ) is obtained as a molded product. The cavity 5 has a relatively flat surface and a vertical rib on the side of the box. The case of molding is shown. In the case of (5), a case is shown in which the surface of the cavity 5 is flat, not a rib structure, and a very flat molded product such as a lens or a disk is formed. In case (5), the cavity 5 has a complicated shape, and a complicated, large, or thick molded product such as an instrument panel or a bumper is formed.

As described above, in FIG.
As the mold clamping pressure is increased from low pressure to high pressure, the mold opening decreases, and tends to move to the left and right with respect to the standard. The inflection points (A, A ′,
A ″) has been found. As a representative example of such experimental results, in the region B where the mold clamping pressure value is smaller than the inflection point A, the movable region is moved by the kinetic energy of the resin flow during injection filling. Since the mold 4b is separated farther than the fixed mold 4a, a large gap is generated between the filled resin and the cavity 5 at the time of the completion of the injection filling. In this case, the flow speed of the resin becomes discontinuous, resulting in defects such as flow marks, etc. In order to eliminate the cause of such defective products, it is extremely necessary to control the injection process and the compression process in an extremely coordinated manner. A difficult molding method is required.

Conversely, in the region C where the mold clamping pressure value is larger than the inflection point A, the kinetic energy of the resin flow during injection filling is reduced without the movable mold 4b relatively moving with respect to the fixed mold 4a. Since the resin can be absorbed, the resin is fully filled (just pack) into the cavity 5 when the injection filling is completed. Further, in the above-mentioned C region, there is no occurrence of defects such as a flow mark because the resin does not reflow even when shifting to the compression step, and it is unnecessary to control the injection step and the compression step in conjunction with each other. Becomes

Based on the above results, in the present embodiment, the region C is selected. That is, even in the region C, in the region where the mold clamping pressure value is large, the resin pressure in the cavity 5 is increased as a result, and the resin pressure in the cavity 5 is reduced, which is one of the advantages in the injection compression molding. The maximum value (upper limit value) of the mold clamping pressure value is defined from the allowable maximum value of the resin pressure in the cavity 5 which is determined to be appropriate from the shape of the molded product and the physical properties of the resin, and the lower limit value is the inflection point. The range with the mold clamping pressure value corresponding to the point A, that is, the region D was set as an appropriate mold clamping pressure value.

Furthermore, the mold opening behavior accompanying the injection filling is a result given by the extension of the tie bar 12, and the set mold clamping force is the same as the extension of the tie bar 12, but is actually applied to the mold. Since the mold clamping force showed a tendency to increase, it was found that the relationship between the injection filling pressure, the mold opening amount, and the mold clamping force acted in a direction to automatically balance.
That is, in the toggle-type mold clamping device 50, when setting the appropriate mold opening amount, even if the condition of the appropriate mold clamping force value is set somewhat rough, the mold clamping force is automatically balanced by extending the tie bar 12, so that it is directly corrected. As compared with the case of the pressure-type mold clamping device, there is also obtained an advantage that the molding control becomes easier. In setting the appropriate mold clamping pressure value described above, the mold opening amount was defined as shown in FIG. 4, but after determining whether or not a defect such as a flow mark was generated by quality inspection of the molded product after molding. It is also possible to find the inflection point A.

After completing the above-mentioned initial setting,
Next, the molding operation starts. FIG. 4 illustrates the process steps in the injection filling step and the compression step. Specifically, the operation is performed as described below. (1) Die height adjustment is performed so as to obtain the appropriate mold clamping force value set earlier. Supply pressure oil to the mold clamping cylinder to perform mold clamping. (Toggle is in a linear state) (2) Injection filling is performed by pressure control based on the injection pressure value set previously. At this time, in the early stage of the injection, the filling speed (injection speed) is increased due to the increase in the flow resistance in the cavity in the late stage of the injection, because the flow resistance in the cavity is small.
Decelerates naturally, resulting in an ideal natural-fill flow having a continuous velocity gradient and generating no pack pressure. (3) In this embodiment, the injection filling control for filling the entire measured value without leaving the cushion amount of the molten resin on the injection side (cutoff state) is used. By doing so, there is no occurrence of a defect due to discontinuity of the resin filling flow due to the holding pressure switching on the injection side. Detection for confirming the completion of injection filling described later is extremely easy and accurate. Metering and injection filling control is also simplified. Further, even in the cutoff state, the molten resin is filled in the passage from the injection nozzle to the cavity 5 with the set injection pressure value, so that the molten resin does not flow backward. Injection filling with the cushion amount remaining is also possible, but in this case, it is necessary to keep the movable mold 4b from moving after the filling pressure setting value on the injection side is completed.

(4) The movable mold 4b is retracted (opened) in a direction away from the fixed mold 4a by extending the tie bar 12 in response to the injection filling. When the injection filling is completed, the mold opening becomes the maximum and the cavity 5
Since the inside of the molten resin is almost fully filled (just pack), and the stretching behavior of the tie bar 12 due to the application of the appropriate mold clamping force acts elastically as if it were a spring, the injection process starts. When switching to the compression step, there is no need to worry about the occurrence of defects such as flow marks, so that special switching timing control is not required. Further, since the tie bar 12 acts resiliently, even if molding conditions such as resin temperature fluctuate during molding, the tie bar 12 acts to absorb the fluctuation, so that there is no variation in quality.

(5) After the injection filling is completed, a compression step is performed on the mold clamping side. The detection of whether or not the injection filling is completed is performed by detecting the change in the operating oil pressure value in the injection cylinder in the above-described cutoff state,
Alternatively, it is determined by a change in the forward movement (injection speed) of the injection piston. That is, the operating oil pressure value in the injection cylinder is controlled to be constant along with the screw advance operation so that the injection filling pressure is constant from the start of injection filling to just before the completion of injection. Therefore, when the injection is completed, that is, when the screw reaches the forward limit, the forward movement of the screw is stopped, so that the operating oil pressure value in the injection cylinder temporarily sharply increases. That is, the completion of injection filling can be accurately detected by detecting the operating oil pressure value in the injection cylinder. However, the present invention is not limited to this, and it may be detected that the injection filling is completed when the screw advance operation or the piston advance operation is stopped. Furthermore, it is also possible to use a method for confirming and detecting the completion of injection filling as described above in combination.

(6) When the completion of the injection filling is detected in this way, the process control timer is started to control the compression process. The holding pressure cooling time or the measurement start time is set in advance in the process control timer. The holding pressure cooling time is set as the holding pressure cooling time (compression completion time) after calculating the cooling and solidifying time of the resin based on the resin temperature, the mold cooling capacity, the shape of the molded product, and the like. Further, the measuring start time is based on the time when the gate is sealed, but in a molding machine in which a shut-off valve is incorporated, it is set based on the shut-off valve closing operation completion time.

(7) As described above, in the compression step, the above-mentioned proper mold clamping pressure value is maintained, thereby coping with the cooling-solidification-shrinkage behavior of the resin by the elastic recovery force of the tie bar 12 stretched by injection filling. The compression operation can be realized, and a high-quality compact with extremely low distortion can be obtained. (8) That is, the maximum value of the mold clamping force at the time of performing compression on the mold clamping side is an initial setting mold clamping force that defines the amount of mold opening during the injection filling process.
The clamping force during the compression process is sufficient to be the same as the clamping force applied by the elastic recovery force of the tie bar 12 to the state of the initial clamping force. Test results have been obtained. For this reason, by maintaining the state of the initial mold clamping force in the compression process, the most appropriate compression action is obtained for the resin, and also in the control, the timing control of the pressure increase of the mold clamping force and the optimal mold clamping force are controlled. No complicated control such as setting is required. In addition, there is no need to modify complicated and high-precision mold clamping cylinders, special hydraulic control valves, hydraulic cylinders for compression apart from toggles, etc. The advantages are extremely large, for example, the failure of the mold and the molding machine due to the addition of unnecessary mold clamping force can be prevented.

[0020]

As is apparent from the above description, in the present invention, the injection filling step and the compression step can be performed by a simple control method of only controlling the injection pressure and the mold clamping pressure. It becomes very easy. Furthermore, because of the pressure control, a high-quality molded product can be stably supplied without being affected by fluctuations in molding conditions other than the pressure during molding. In addition, by using injection pressure control that allows injection filling,
The ideal injection filling control that has a continuous speed gradient according to the product shape, does not generate pack pressure, and enables short-time filling can be set very easily and automatically, so control operability is extremely easy. It is. Even when the injection filling is completed, the molten resin is in a just-packed state, so that there is no defect such as a flow mark caused by the discontinuity of the resin flow. Since timing control is not required, operability of control can be further simplified. Also in the compression step, a compression action corresponding to the cooling, solidification, and shrinkage of the resin is provided, so that residual distortion and deformation can be extremely reduced, and a molded article of extremely high quality can be obtained. Since the compression action from the mold clamping side is added continuously and fluidly from the completion of injection filling to the switching of the compression process, the control of the compression process and the start of weighing after switching are simple control using a timer. As a result, the control system is extremely simple and the controllability of the molding is very easy. It is possible to perform high-precision injection compression molding without applying any special auxiliary equipment and modification to the existing injection molding device of the toggle-type mold clamping device.

[Brief description of the drawings]

FIG. 1 is an overall side view of an injection molding apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a correlation between a set mold clamping force and a tie bar elongation amount according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a correlation between a mold opening amount of a mold and a set mold clamping pressure according to the embodiment of the present invention.

FIG. 4 is an explanatory view of a process of injection compression molding according to an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Link housing 2 Fixed board 3 Movable board 4 Die 4a Fixed mold 4b Movable mold 5 Cavity 6 Toggle mechanism (or toggle) 6a, 6b, 6c Link 7 Crosshead 8 Mold clamping cylinder 9 Piston rod 10 Guide rod 12 Tie bar 50 Mold clamping device 100 Injection molding device

Claims (1)

(57) [Claims] In an injection molding apparatus which performs mold clamping by a mold clamping device having a toggle mechanism, an injection pressure capable of filling a mold with a resin amount obtained by adding a cooling solidification shrinkage calculated in advance during an injection filling step. In the state where the toggle of the mold clamping device is maximally extended, the tie bar is extended to the mold opening amount corresponding to the cooling solidification shrinkage amount by the pressure of the resin filled in the mold cavity while the toggle of the mold clamping device is maximally extended. Injection compression molding characterized in that a mold clamping force that allows the mold to open is pre-loaded on the mold, and in the compression step after the injection filling is completed, the mold is closed by the elastic recovery force of the tie bar. Method.