JP6599825B2 - Injection molding method and injection molding apparatus - Google Patents

Description

  The present invention relates to an injection molding method and an injection molding apparatus for injecting and molding a molten synthetic resin material into a cavity in a state where a fixed mold and a movable mold are closed and clamped.

  With regard to this type of injection molding apparatus, for example, Patent Literature 1 proposes a technique that can improve filling properties without causing molding defects such as burrs.

Japanese Patent Laid-Open No. 7-1525

  However, according to Patent Document 1, during the transition from the injection process to the pressure holding process, the injection pressure is set to P2 higher than the set pressure for the time t2, but after the time t2 has elapsed, this injection is performed. Since the pressure is drastically lowered, burrs are generated, the surface of the molded product is roughened, and the quality of the molded product is deteriorated, and the molded product is easily deformed due to residual stress.

  Therefore, in view of the above points, the present invention aims to improve the quality of a molded product without increasing the molding cycle time as much as possible even in a molded product with a small thickness.

Therefore, the first invention is an injection molding method for injecting and molding a molten synthetic resin material into a cavity in a state where the fixed mold and the movable mold are closed and clamped.
The mold is clamped by the mold clamping mechanism ,
After clamping by the clamping mechanism is performed, based on the detection output of the injection pressure detecting device, and reach the maximum clamping force of the mold clamping mechanism within the mold internal pressure does not exceed the injection pressure until the injection pressure without the range reaches the setting value set in advance for lowering the mold internal pressure to reach the set value or also the injection pressure or raising the mold internal pressure is set in advance The injection operation is performed while the first control device controls to repeat the set number of times,
After being controlled by the first control device to repeat the set number of times, the in- mold pressure that has risen all at once when the in-mold pressure exceeds the injection pressure is detected by the injection pressure detecting device. When the second controller determines that the maximum mold clamping force has been reached based on the output, the pressure holding operation is controlled,
After the pressure holding operation and the injection operation are finished, the synthetic resin material is cooled and solidified, and then the mold is opened to take out the molded product.

According to a second aspect of the invention, there is provided an injection molding apparatus for injecting and molding a molten synthetic resin material into the cavity in a state where the fixed mold and the movable mold are closed and clamped.
A mold clamping mechanism for clamping,
An injection pressure detecting device for detecting the injection pressure;
After the mold clamping is performed by the mold clamping mechanism, the mold clamping mechanism is within a range in which the pressure inside the mold does not exceed the injection pressure based on the detection output of the injection pressure detecting device when performing the injection operation. wherein until the respective set value maximum-type the mold or in likewise the injection pressure or the pressure increased up to the injection pressure within a range that does not lead to the clamping force reaches the respective set value set in advance is set in advance A first control device for controlling to lower the in-mold pressure repeatedly for a set number of times;
After being controlled to repeat the set number of times by the first control device, the in- mold pressure that has risen all at once when the in-mold pressure exceeds the injection pressure is detected by the injection pressure detecting device. A second control device is provided that performs control so as to perform a pressure holding operation when it is determined that the maximum clamping force has been reached based on the output.

  According to the present invention, it is possible to improve the quality of a molded product even in a molded product with a small thickness without increasing the molding cycle time as much as possible.

It is a schematic explanatory drawing of the injection molding apparatus which makes it fracture partially. It is a control block diagram of an injection molding apparatus. It is a figure which shows the timing chart which concerns on injection molding operation | movement.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 3. First, in FIG. 1, reference numeral 1 denotes an injection molding apparatus, which is a thermoplastic synthetic resin melted in a cavity (molding space) formed by both molds with the fixed mold 4 and the movable mold 5 closed. The material is injected to form a thin plate product. In this embodiment, the type of the synthetic resin material is a thermoplastic synthetic resin. However, any type of the synthetic resin material can be applied to a thermosetting synthetic resin, and a foaming agent is mixed into the synthetic resin material to mix bubbles. It can also be applied to foam molding for molding soft synthetic resin.

  An injection mechanism 2 includes an injection cylinder 6 provided with an injection nozzle 7 at an end, and a hopper for supplying a synthetic resin material to the injection cylinder 6 on the upper portion of the base housing 8 at the rear of the injection cylinder 6. 9 is provided. A heater for heating and melting the supplied synthetic resin material is wound around the outer periphery of the injection cylinder 6, and a screw (not shown) rotates and slides in the cylindrical injection cylinder 6. It is stored freely.

  An injection drive unit 10 includes a rotation motor 11 for rotating the screw, a mechanism for rotating the screw, an injection motor 12 that can be rotated forward and backward for moving the screw in the horizontal direction, a mechanism for moving the screw, and the like. I have. The rotary motor 11 and the injection motor 12 are provided with encoders 13 and 14 as position detecting devices. The encoders may be either built in the motor or externally attached. But you can.

  Next, the mold mechanism part 3 schematically shown in FIG. 1 will be briefly described. The fixed die 4 is attached to the fixed die plate 15 via the attachment plate 16, and the movable die 5 is attached to the moving die plate 17 via the attachment plate 18, the spacer 23, the attachment plate 24 and the like. A tie bar 20 is disposed between the fixed die plate 15 and a mold clamping mechanism 19 including a tailstock and a forward / reversely movable motor 21 so that the movable die plate 17 is slidable (movable). It is arranged.

  Accordingly, by operating the mold clamping mechanism 19 including the moving motor 21, mold operations such as mold opening and mold clamping can be performed. In addition, although description is abbreviate | omitted about the structure of the said mold mechanism part 3 containing this mold clamping mechanism part 19, there are various systems, such as a direct acting system other than a toggle system, and the form is not ask | required.

  The moving motor 21 is provided with an encoder 22 as a position detecting device, but this encoder may be either built in the motor or externally attached.

  Next, based on FIG. 2 which is a control block diagram of the injection molding apparatus 1, first, 30 is a control apparatus that performs overall control of operations related to injection molding of the synthetic resin material of the injection molding apparatus 1, 31 Is a storage device connected to the control device 30 for storing and storing various data.

  The control device 30 is connected to the moving motor 21, the rotation motor 11, and the injection motor 12 via an interface 33 and drive circuits 34, 35, and 36, respectively. That is, the control device 30 drives the moving motor 21 via the drive circuit 34, drives the rotation motor 11 via the drive circuit 35, and the injection motor 12 via the drive circuit 36. The drive is controlled.

  Reference numeral 37 denotes an injection pressure sensor as an injection pressure detection device, which detects the pressure applied to the tip of the screw when the synthetic resin material is injected into the cavity.

  Hereinafter, the injection molding operation of the injection molding apparatus 1 having a maximum mold clamping force of, for example, 300 tons will be described with reference to FIG. 3 showing a timing chart relating to the injection molding operation. The present invention can also be applied to an injection molding apparatus that is not limited to 300 tons.

  The horizontal axis in FIG. 3 is time, the unit is second, the vertical axis is pressure, and the unit is ton. In the line graph of FIG. 3, the solid line indicates the injection pressure, and the dotted line indicates the mold clamping force or the mold. Indicates internal pressure. Further, the number of each injection span and each mold clamping span is not limited to the number shown in FIG. 3, and the injection pressure, mold clamping force or in-mold pressure shown in each span is not limited to that shown in FIG. The shape is selected according to the shape of the fixed mold 4 and the movable mold 5 and the type of the molded product. Further, the increase or decrease of the in-mold pressure is repeated as many times as necessary within a range where the in-mold pressure does not exceed the injection pressure and does not reach the maximum mold clamping force. It is not restricted to embodiment shown.

  First, the mold clamping operation is started under the condition that the fixed mold 4 is always maintained at a predetermined temperature according to the synthetic resin material by a heating device (not shown). The fastening operation is performed by driving the moving motor 21 controlled by the control device 30 via the interface 33 and the driving circuit 34.

  In this case, based on the detection output of the encoder 22 (feedback to the drive circuit 34), the control device 30 moves the movable mold 5 first at a high speed and then at a low speed by a corresponding distance. The mold clamping operation is terminated while maintaining the low speed for protecting the mold.

  The mold clamping force at which this mold clamping operation is performed is set according to the shape of the fixed mold 4 and the movable mold 5 and the type of the molded product, and is 10% of 300 tons of the maximum mold clamping force described above. In this embodiment, which is -40% or less, for example, it is about 80 tons. This is because when molding thin molded products that have become the mainstream recently, the pressure in the mold is difficult to escape and difficult to inject, so it is necessary to inject at a low pressure, and the synthetic resin material moves while moving Since it becomes difficult to fill because it cools, the mold clamping operation before the injection operation is performed with the above-mentioned mold clamping force (about 80 tons) with an appropriate mold clamping force selected.

  After the mold clamping operation, the control device 30 controls the injection mechanism unit 2 so as to start injection of the synthetic resin material. Thereafter, in each of the injection spans A, B, C, and D, In each of the mold clamping spans A, B, C, and D, the injection mechanism 2 and the mold mechanism 3 are controlled to perform an injection molding operation.

  That is, the control device 30 drives the rotation motor 11 of the injection mechanism unit 2 through the interface 33 and the drive circuit 35 to rotate the screw in the injection cylinder 6, and from the hopper 9. Since the charged synthetic resin material has already been melted and accumulated at the tip of the injection cylinder 6 (weighed), the control device 30 first connects the injection motor 12 to the interface 33 and the drive circuit 36. When the screw is moved forward by driving through the molten plastic, the molten synthetic resin material accumulated at the tip of the injection cylinder 6 is transferred from the injection nozzle 7 through a sprue bush, a sprue, and a gate. Injection into the cavity is started.

  In the present embodiment, the injection motor 12 related to the injection of the synthetic resin material is driven to rotate at a constant speed except for the start of injection and the stop of the injection, and the screw moves. For example, when the pressure in the mold does not increase or is difficult to increase when the pressure in the mold is increased, the control device 30 causes the injection motor 12 to increase the rotation speed. The pressure inside the mold may be increased by control.

  Then, as described above, the control device 30 monitors the injection pressure on the basis of the detection output from the injection pressure sensor 37 in a state where the mold is clamped without reaching the maximum mold clamping force. However, the injection operation is performed by controlling the pressure in the mold.

  That is, since the first set value (the injection pressure level at the point P1 in FIG. 3) of the injection pressure obtained and set by conducting flow analysis in advance is already stored in the storage device 31, the injection operation When the control device 30 determines based on the output from the injection pressure sensor 37 that the injection pressure increased from the in-mold pressure with the injection reaches the injection pressure level at the point P1, first, The control device 30 controls to lower the in-mold pressure that has risen due to the injection.

  That is, for example, due to the structure of the movable mold 5, the cavity forming surface 5A of the movable mold 5 is bent outwardly so that the amount of bending becomes larger at the center, thereby increasing the volume in the cavity. Or the control device 30 drives the moving motor 21 to move the movable die 5 by a first predetermined distance stored in advance in the storage device 31 so that the in-mold pressure is injected. Control is performed so that the pressure inside the mold is increased by the injection by escaping from the molding apparatus 1. In this way, the control device 30 adjusts so as to reduce the pressure inside the mold, and controls so that the injection pressure does not increase.

  As described above, when the injection pressure reaches the injection pressure level at the point P1, the control device 30 controls the mold pressure so as to decrease and immediately decreases the mold pressure. The movable mold 5 is returned to the original state so as to eliminate the bending of the cavity forming surface 5A of the movable mold 5 or moved by moving the moving motor 21 in the reverse direction. Move to close.

  The first set value of the injection pressure described above is set according to the type of the mold or the molded product, and is 20% to 70% of the maximum clamping force of 300 tons, for example, about 150 tons, which is about half. is there. This is because, as described above, when molding a thin molded product that has become the mainstream recently, the gas in the mold is difficult to escape and injection is difficult. Since the material cools while moving, it becomes difficult to fill, so the appropriate first set value is selected. If it is set too high, burrs are likely to occur in the molded product. It is set so as not to.

  As described above, when the control device 30 determines that the injection pressure has reached the injection pressure level at the point P1 based on the output from the injection pressure sensor 37, the control device 30 causes the in-mold pressure to decrease. The injection pressure is also lowered by the decrease in the mold pressure. In this case, the pressure inside the mold is controlled so as not to exceed the injection pressure.

  Then, the injection pressure also decreases due to the decrease in the in-mold pressure, and the second preset value of the injection pressure (the injection pressure level at the point P2 in FIG. 3), that is, the output from the injection pressure sensor 37 is obtained. When the control device 30 determines that the second set value set to a value several percent lower than the first set value is reached, the control device 30 causes the injection pressure so that no burrs are generated in the molded product. Control to increase the pressure in the mold at a level not exceeding.

  That is, in order not to lose the injection pressure, the movable mold 5 is fixed so as not to move, or the moving motor 21 is driven to advance the second predetermined distance stored in the storage device 31 in advance. The movable mold 5 is slightly moved so as to be closed, and the pressure in the mold is increased.

  As described above, when the injection pressure reaches the injection pressure level at the point P2, the control device 30 controls the mold pressure so that the mold pressure increases. The movable mold 5 is moved by the above-mentioned second predetermined distance that is moved by driving the moving motor 21 immediately after the mold 5 is kept stationary so that the mold 5 does not move or the pressure inside the mold is increased. Move to open.

  Then, as described above, the injection pressure also increases by increasing the in-mold pressure, and based on the output from the injection pressure sensor, the third set value of the injection pressure level (point P3 in FIG. 3). When the control device 30 determines that the injection pressure level has been reached, the control device 30 controls to lower the mold.

  That is, as described above, for example, the cavity forming surface 5A of the movable mold 5 is bent outwardly so that the amount of bending becomes larger at the center portion due to the structure of the movable mold 5, etc. Or the control device 30 drives the moving motor 21 to move the movable mold 5 slightly by a third predetermined distance stored in the storage device 31 in advance. Control is performed so that the pressure inside the mold is released to the outside of the injection molding apparatus 1 and the pressure inside the mold that has been raised by the injection is lowered. In this way, the control device 30 adjusts so as to reduce the pressure inside the mold, and controls so that the injection pressure does not increase.

  As described above, when the injection pressure reaches the injection pressure level at the point P3, the control device 30 controls the pressure in the mold to decrease and immediately decreases the pressure in the mold. The movable mold 5 is returned to its original state so that the cavity forming surface 5A of the movable mold 5 is not bent, or is moved by moving the moving motor 21 in the reverse direction. Move 5 to close.

  As described above, the control device 30 controls the in-mold pressure based on the output from the injection pressure sensor 37 while monitoring the injection pressure. Corresponding to the injection pressure level of P9, the mold pressure is controlled to be raised or lowered within a range where the pressure inside the mold does not exceed the injection pressure and within the range where the maximum mold clamping force is not reached. An injection operation is performed.

  When the in-mold pressure is increased so as to be at the levels of the points P1, P3, P5, and P7, the control is performed so as to increase the rotation speed if it does not increase or is difficult to increase. The device 30 may control the injection motor 12 to increase the in-mold pressure.

  Then, by controlling in this way, when the pressure inside the mold exceeds the injection pressure and the level of the injection pressure reaches the level of the point P10, the pressure inside the mold approaches the above-described maximum mold clamping force, Since the injection pressure increases rapidly, the pressure inside the mold also increases (rapidly) at once.

  Therefore, when the pressure inside the mold reaches the maximum clamping force while the pressure inside the mold exceeds the injection pressure, the controller 30 is controlled to start the pressure holding operation. (The driving of the injection motor 12 is controlled so as to continue the injection operation). This holding pressure is a pressure that is applied until the portion in the gate is solidified at a constant pressure so that the synthetic resin material does not flow backward from the gate after the entire cavity is filled with the molten synthetic resin material. By this pressure holding operation, the synthetic resin material in the cavity can be compressed to increase the compression density uniformly and uniformly.

  Therefore, when the filling rate of the synthetic resin material into the cavity is increased, the burrs are generated when the in-mold pressure is defeated by the injection pressure. As described above, the in-mold pressure is reduced. Since the pressure holding operation is performed by setting the pressure higher than the injection pressure at a stroke to reach the maximum clamping force, burrs are not generated in the molded product, and the quality of the molded product is improved.

  Eventually, when a predetermined amount of a synthetic resin material weighed in advance is injected into the cavity, the control device 30 determines the injection motor 12 based on the output of the injection pressure sensor 37 that the injection pressure has become zero. The driving is stopped and the injection operation is terminated, and the pressure holding operation is also terminated. Thereafter, as described above, the control device 30 rotates the screw in the injection cylinder 6 by driving the rotation motor 11 of the injection mechanism section 2 through the interface 33 and the drive circuit 35. A predetermined amount of the synthetic resin material charged from the hopper 9 is accumulated at the tip of the injection cylinder 6 (weighing for the next injection), and the fixed mold 4 is cooled by a cooling device (not shown). Then, the synthetic resin material is solidified.

  Then, in the mold clamping spans F and G, the measurement for the next injection as described above and the solidification of the synthetic resin material cooled to the extent that it can be taken out from the fixed mold 4 and the movable mold 5 as molded products are finished. Then, the control device 30 stops the cooling by the cooling device and starts the mold opening operation.

  That is, the mold opening operation by the movement of the movable mold 5 is performed by the control device 30 being controlled and driven by the control motor 30 via the interface 33 and the drive circuit 34.

  In this case, based on the detection output of the encoder 22 (feedback to the drive circuit 34), the control device 30 moves the movable mold 5 at a low speed first and then at a high speed by a corresponding distance, Move the mold at low speed to protect the mold and finish the mold opening operation. As described above, when the movable mold 5 finishes moving at a low speed first, the pressure in the mold becomes zero.

  When the mold opening operation is completed, the control device 30 moves the ejector pin to release the molded product, and removes the thin plate-shaped molded product from the cavity to prepare for the production of the next molded product.

  The control device 30 repeats the required number of times to increase or decrease the mold pressure within a range where the mold pressure does not exceed the injection pressure and within the range where the maximum mold clamping force is not reached. The first control device to be controlled, and the in-mold pressure that has risen all at once when the in-mold pressure exceeds the injection pressure reaches the maximum mold clamping force based on the detection output of the injection pressure detection device If it is determined, it may be configured by two control devices separately from the second control device that controls to perform the pressure holding operation.

  As described above, according to the present embodiment, it is possible to improve the quality of a molded product without increasing the molding cycle time as much as possible even in a molded product having a small thickness. That is, it is a synthetic resin molding performed at an in-mold pressure that does not reach the maximum clamping force at the time of injection of the synthetic resin material, and in particular, it is possible to perform the secondary processing-less of thin-wall molding and foam molding that increases the pressure. . Even in a thin molded product, the synthetic resin material can be filled into the cavity without pressure loss, and pressure is not excessively applied to the synthetic resin material filled in the cavity, so that the resin density is as much as possible. Residual stress can be reduced without bias, and necessary high-pressure and high-speed injection can be easily performed in foam molding.

  As described above, the embodiments of the present invention have been described. However, various alternatives, modifications, and variations can be made by those skilled in the art based on the above description. Including alternatives, modifications or variations.

DESCRIPTION OF SYMBOLS 1 Injection molding apparatus 2 Injection mechanism part 3 Clamping mechanism part 4 Fixed mold 5 Movable mold 19 Clamping mechanism part 30 Control apparatus 37 Injection pressure sensor

Claims (2)

In an injection molding method of injecting and molding a molten synthetic resin material into a cavity in a state where the fixed mold and the movable mold are closed and clamped,
The mold is clamped by the mold clamping mechanism ,
After clamping by the clamping mechanism is performed, based on the detection output of the injection pressure detecting device, and reach the maximum clamping force of the mold clamping mechanism within the mold internal pressure does not exceed the injection pressure until the injection pressure without the range reaches the setting value set in advance for lowering the mold internal pressure to reach the set value or also the injection pressure or raising the mold internal pressure is set in advance The injection operation is performed while the first control device controls to repeat the set number of times,
After being controlled by the first control device to repeat the set number of times, the in- mold pressure that has risen all at once when the in-mold pressure exceeds the injection pressure is detected by the injection pressure detecting device. When the second controller determines that the maximum mold clamping force has been reached based on the output, the pressure holding operation is controlled,
An injection molding method characterized in that after the pressure holding operation and the injection operation are completed, the synthetic resin material is cooled and solidified, and then the mold is opened to take out a molded product. In an injection molding apparatus for injecting and molding a molten synthetic resin material into a cavity in a state where the fixed mold and the movable mold are closed and clamped,
A mold clamping mechanism for clamping,
An injection pressure detecting device for detecting the injection pressure;
After the mold clamping is performed by the mold clamping mechanism, the mold clamping mechanism is within a range in which the pressure inside the mold does not exceed the injection pressure based on the detection output of the injection pressure detecting device when performing the injection operation. wherein until the respective set value maximum-type the mold or in likewise the injection pressure or the pressure increased up to the injection pressure within a range that does not lead to the clamping force reaches the respective set value set in advance is set in advance A first control device for controlling to lower the in-mold pressure repeatedly for a set number of times;
After being controlled to repeat the set number of times by the first control device, the in- mold pressure that has risen all at once when the in-mold pressure exceeds the injection pressure is detected by the injection pressure detecting device. An injection molding apparatus comprising: a second control device that controls to perform a pressure holding operation when it is determined that the maximum mold clamping force has been reached based on an output.

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