JPH06297522A - Gas injection molding method and its metal mold - Google Patents

Abstract

PURPOSE:To provide a gas injection molding method which can mold excellently a large sized facial product and by which a load for manufacture of the metal mold is reduced, and the metal mold. CONSTITUTION:A cylindrical auxiliary cavity 24 interconnected to a main cavity 23 of a metal mold 20, a piston like movable metal mold part 40 made freely movable inside the auxiliary cavity 24, and a spacer 43 which controls the movable metal mold part 40 so as to retreat backward from any intermediate position, are provided. The cavity is filled with resin 30 to a flow end position while a volume of the resin 30 to be extruded into the auxiliary cavity 24 is controlled by filling under a state wherein the auxiliary cavity 24 is closed with the movable metal mold part 40. Further, by injecting gas by making the movable metal mold part 40 be of an open state a gas channel 32 is formed to a passage end position to improve moldability of a molded item 31.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas injection molding method and a mold thereof, and can be used for molding interior and exterior parts such as automobile bumpers and dashboards, or large surface products such as casings of home electric appliances. .

[0002]

2. Description of the Related Art Conventionally, a gas injection molding method has been known as an injection molding method capable of obtaining a lightweight and highly rigid molded product (JP-A-3-138126). In this method, after injection of a molten resin into the main cavity in the mold, an inert gas such as pressurized nitrogen gas is injected into the cavity for injection molding. A gas flow path (hereinafter referred to as a "gas channel") is formed in the filled molten resin by gas pressure, and the molten resin pressed by the gas in the gas channel communicates with the outside of the mold. Since it is discharged to (hereinafter referred to as "auxiliary cavity"), a uniform thin hollow molded product can be obtained. By this gas injection molding, it is attempted to mold a large-sized molded product used for the interior and exterior of automobile bumpers and dashboards.

[0003]

In such gas injection molding, if the shape of the molded product is a plane, the wall thickness of the molded product becomes thin and the filled resin has a viscosity due to solidification by cooling. To increase. Due to this increase in viscosity, a high gas pressure is required in order to form the gas channel up to the gas flow path end position and completely fill the cavity with resin. However, when the gas is injected at a high gas pressure,
There is a problem that gas invades other than the gas channel guide portion and impairs the appearance and function of the molded product. Further, in molding a large-sized molded product, in order for the communicating portion that communicates the main cavity and the auxiliary cavity to function as planned, it is necessary to perform a finishing operation for finely adjusting the inner diameter of the communicating portion to a proper size. Since this finishing work is delicate, many trials and errors are required to complete the mold, and there is a problem that it becomes a heavy burden in manufacturing the mold. That is, if the inner diameter of the communication part is too large, the resin filled in the main cavity will enter the auxiliary cavity through the communication part before the gas is injected, and the auxiliary cavity will not be able to exhibit its original function during gas injection. . On the other hand, if the inner diameter of the communicating part is too small, the molten resin will not be sufficiently discharged to the auxiliary cavity under normal gas pressure, and if the gas pressure is increased to compensate the amount of molten resin discharged, a stable gas channel is formed. Will be difficult. Therefore, in order to finish the die, it is necessary to repeat trial and error such as finely adjusting the communicating portion while actually performing molding of the resin, and this finishing work is a heavy burden in manufacturing the die. .

It is an object of the present invention to provide a gas injection molding method and a mold for the same, which can reduce the load of manufacturing the mold and can favorably mold a large surface article.

[0005]

According to the gas injection molding method of the present invention, after the molten resin is filled into the main cavity of the mold, a pressurized gas is injected into the main cavity so that the inside of the molten resin is filled. A gas injection molding method in which injection molding is performed while forming a gas channel that is a passage for a pressurized gas in
A cylindrical auxiliary cavity that communicates with the main cavity is provided at the end of the gas channel, and the internal volume of the auxiliary cavity is made variable so that the internal volume of the movable mold part is reduced. When the pressurized gas is injected into the main cavity after the filling of the molten resin is started, the inner volume of the movable mold part is expanded by time control.

In the injection molding die of the present invention, after starting the filling of the molten resin into the main cavity inside, a pressurized gas is injected into the main cavity so that a passage for the pressurized gas is introduced into the molten resin. A metal mold for gas injection molding for forming a gas channel while forming a gas channel, comprising: a cylindrical auxiliary cavity communicating with the main cavity; and an inner volume of the auxiliary cavity that moves back and forth inside the auxiliary cavity. And a retractable control means for controlling the movable die part to retract backward from an arbitrary intermediate position.

[0007]

In the present invention as described above, the movable mold is moved forward to close the auxiliary cavity, and the molten resin is charged in a state where the inner volume of the auxiliary cavity is reduced. However, there is no inconvenience such as molten resin entering the auxiliary cavity. As a result, the molten resin can be pushed into the main cavity under high pressure and filled up to the flow end position of the resin. After the start of filling, the movable mold part can be retracted, the movable mold part is retracted by gas pressure, etc., and the pressurized gas is injected into the molten resin while the internal volume of the auxiliary cavity is expanded, and the pressurized gas is injected. Is injected into the molten resin along the gas channel guide portion to form a passage for the pressurized gas. Here, since the pressurized gas can move toward the end position of the passage while pushing the molten resin into the auxiliary cavity due to the expansion of the inner volume of the movable mold part, the gas channel is set in the passage set in the main cavity. It is reliably formed up to the end position. Further, if the retracting position of the movable mold part can be arbitrarily controlled by the retracting control means, the gas channel formed in the molten resin is controlled and adjusted so that the volume becomes a proper size. As a result, the volume of the gas channel does not increase as the gas channel reaches the flow end position of the molten resin,
A hole is prevented from being formed at the position, and the volume of the gas channel is not reduced so much that the gas channel does not reach the vicinity of the flow end position of the molten resin at all, and the sink mark is generated near the position. It is also prevented from occurring. For this reason, in order to comply with the size and length of the gas channel or the crystallinity / amorphism of the material used, it is not necessary to finish the die for adjusting the volume of the auxiliary cavity itself, and the die It also eliminates the need for delicate finishing work to finely adjust the communication part, significantly reducing the burden on the mold manufacturing work, and at the same time makes it possible to stably obtain good molded products. To be achieved.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an injection molding machine 1 according to the first embodiment of the present invention. The injection molding machine 1 includes an injection device 10 that injects a synthetic resin and a mold 20 that is a mold for molding. The injection device 10 is one in which a molten resin 30 is kneaded with a screw 12 inside a cylindrical barrel 11. A nozzle 13 is provided at the tip of the barrel 11. The nozzle 13 is adapted to be connected to the bush 21 of the mold 20. The injection molding machine 1 uses the bush 21 for the molten resin 30 injected from the nozzle 13.
The molded product 31 is molded by filling the mold 20 through the sprue 22 formed in the central portion of the mold. nozzle
A blow-in pipe 14 for injecting a pressurized gas is inserted inside 13. The blow-in pipe 14 is supplied with an inert gas such as nitrogen gas from a supply source (not shown) to form a gas channel 32 inside the molded product 31.

The mold 20 is formed by connecting an auxiliary cavity 24 to a main cavity 23 which is filled with a molten resin 30 for molding. As shown in FIG. 2, the main cavity 23 is formed by forming gas channel guide portions 26 on both sides of a substantially rectangular thin plate portion 25. The gas channel guide portion 26 is provided over the entire length of the main cavity 23 so that the gas channel 32 can be reliably formed up to a position (hereinafter referred to as “passage end position”) A set as an end position of the gas channel 32. And the thickness is thin
It is thicker than 25.

The auxiliary cavity 24 has a cylindrical shape whose inner surface extends in the vertical direction, and is provided in the extending direction of the gas channel guide portion 26 so that the main molten resin 30 flows linearly. A communication portion 27 is provided at the entrance of the auxiliary cavity 24, and the communication portion 27 allows the main cavity 23
Is connected with. Inside the auxiliary cavity 24, a piston-shaped movable mold part 40 is installed so as to be movable back and forth.

That is, the movable mold part 40 is formed in a flat cross section corresponding to the auxiliary cavity 24 so as to be movable inside the auxiliary cavity 24 in the vertical direction in the figure. In order to drive the movable mold part 40 to move back and forth, a hydraulic cylinder device 41 as a driving means is provided, and the plunger 42 of the hydraulic cylinder device 41 is provided with a movable mold part.
It is connected to the bottom of 40. As a result, the movable mold part 40
Is moved to the upper end position C of the auxiliary cavity 24 to close the auxiliary cavity 24, as shown in FIG. Between the movable mold part 40 and the hydraulic cylinder device 41, a plurality of spacers 43 as a retreat control means can be inserted. A plurality of spacers 43 having the same thickness and different spacers are prepared to form a spacer group. Each spacer 43 is provided with a cutout portion 44 through which the plunger 42 of the hydraulic cylinder device 41 is inserted. By selecting a suitable number of spacers having a proper thickness from the spacer group and inserting them between the movable mold part 40 and the hydraulic cylinder device 41, the movable mold part 40 is shown in FIG. Thus, the upper surface thereof can be controlled so as not to move backward from the arbitrary intermediate position D.

The procedure of injection molding in this embodiment will be described below. First, from the amount of the molten resin 30 to be extruded into the auxiliary cavity 24 in advance, the position of the rearmost part of the movable mold part 40 that can be retracted is determined, and the spacer required to regulate the retracting of the movable mold part 40 at that position 43 is selected from the spacer group, and the selected spacer 43 is installed in the mold 20. Next, as shown in FIG. 3, the movable mold part 40 is advanced to operate the injection device 10 with the auxiliary cavity 24 closed, and the molten resin 30 is pushed into the main cavity 23.
By pushing in 30, the molten resin 30 is filled up to the flow end position B of the resin. Here, since the auxiliary cavity 24 is closed by the movable mold part 40, there is no possibility that the molten resin 30 will be pushed into the auxiliary cavity 24, so that it is surely filled up to the flow end position. Filling can be performed with the filling pressure of the molten resin 30 set sufficiently high.

Next, as shown in FIG. 4, high pressure gas is injected into the main cavity 23 with the movable mold part 40 retracted and the auxiliary cavity 24 opened. The injected high-pressure gas advances inside the molten resin 30 along the gas channel guide portion 26. At this time, since the auxiliary cavity 24 is in the open state, even if the molten resin 30 is filled up to the flow end position B of the resin, the high-pressure gas can proceed while pushing the molten resin 30 into the auxiliary cavity 24.
32 is reliably formed up to the passage end position A set in the main cavity 23.

Subsequently, after the mold 20 is appropriately cooled, the molded product 31 is taken out from the mold 20 and thereby the injection molding is completed. Here, the high-pressure gas reaching the passage end position A is
With sufficient strong pressing force, mold the entire surface of molten resin 30
Since the molded product 31 taken out from the mold 20 is brought into close contact with the inner surface of the mold 20 and the close contact is maintained, defective parts such as sink marks do not occur.

According to this embodiment as described above, there are the following effects. That is, since the movable mold part 40 is moved forward to fill the molten resin 30 with the auxiliary cavity 24 closed, even if the filling pressure of the molten resin 30 becomes high, the auxiliary cavity is injected before the gas is injected. Since there is no inconvenience such as the molten resin 30 entering the 24, the molten resin 30 can be pushed into the main cavity 23 under a high pressure, and the molten resin 30 can be reliably filled up to the flow end position B.

After the filling is completed, the movable mold part 40 is retracted to open the auxiliary cavity 24, and
Since the high-pressure gas is injected into the molten resin 30, even if the molten resin 30 is filled up to the flow end position B of the resin, the high-pressure gas can move while pushing the molten resin 30 into the auxiliary cavity 24. Because the gas channel 32
Can be reliably formed up to the passage end position A set in the main cavity 23. Therefore, the high-pressure gas reaching the passage end position A causes the entire surface of the molten resin 30 to adhere to the inner surface of the mold 20 with a sufficiently strong pressing force, and maintains this contact state. Since defective parts such as sink marks are not generated in the molded product 31 thus formed, the moldability of injection molding can be improved.

Further, since the retracted position of the movable mold part 40 can be restricted to an arbitrary position by the spacer 43, the gas channel 32 formed in the molten resin 30 has an appropriate volume. Can be adjusted. Therefore, the volume of the gas channel 32 does not become excessively large as it reaches the flow end position of the molten resin 30, and a hole is prevented from being formed at the position of the molded article 31, and the molten resin 30 is prevented. As the gas channel 32 does not reach the vicinity of the flow end position at all, the volume of the gas channel does not become too small, and sink marks are prevented from occurring in the vicinity of the position. Moldability can be improved.

Further, since the inflow of the molten resin 30 into the auxiliary cavity 24 is controlled by advancing and retracting the movable mold part 40, it is fine to finely adjust the communicating part of the mold as in the conventional case. Since finishing work is unnecessary and the substantial volume of the auxiliary cavity 24 can be changed by the spacer 43, it is not necessary to modify the mold for changing the capacity of the auxiliary cavity 24, and it is possible to improve the mold manufacturing work. The burden can be significantly reduced.

A second embodiment of the present invention is shown in FIGS. The second embodiment is a passive movable mold in which the active movable mold part 40 driven by the hydraulic cylinder device 41 in the first embodiment is urged to the position side where the auxiliary cavity 24 is closed. Part 50. That is, in FIG. 5, the movable mold part 50 provided in the auxiliary cavity 24 has a conical head portion 51, and even if the movable mold part 50 is in a closed state, the head 51 does not have a metal mold. The pressure of the high pressure gas injected into the mold 20 is applied.
One end of a coil spring 53 as a biasing means is connected to the bottom surface 52 of the movable mold part 50. The coil spring 53 biases the auxiliary cavity 24 toward the position C where the auxiliary cavity 24 is closed, and the other end of the coil spring 53 is abutted on the spacer 54 which is stacked. The spacer 54 adjusts the urging force according to the number of the spacers 54, and as shown in FIG. 6, the movable mold part 50 is retracted so that the movable mold part 50 does not retract backward from an arbitrary intermediate position D. It controls the position. Here, the biasing force of the coil spring 53 does not allow the movable mold part 50 to retreat with the pressing force of the molten resin 30 to be filled during the injection molding, and is movable with the pressing force of the injected high-pressure gas. The strength is set to allow the mold part 50 to retract. As a result, the closed state of the auxiliary cavity 24 can be maintained when the molten resin 30 is filled, and the auxiliary cavity 24 can be opened when the high-pressure gas is injected.

In this embodiment as well, the same actions and effects as those of the first embodiment can be obtained, and since the driving means such as the hydraulic cylinder device can be omitted, the entire structure of the injection molding machine can be simplified. The effect of being able to do something can be added.

Next, the effects of the present invention will be described based on concrete experimental examples. [Experimental Example] This experimental example is an experiment in which gas injection molding is performed using the mold according to the present invention. As the mold, the first
A mold having basically the same structure as the mold 20 shown in the embodiment is adopted, and a main cavity 23 in FIG.
A large planar body having the external shape shown as was molded. [Comparative Example] This comparative example is an experimental example performed for comparison with the above experimental example, and injection molding is performed using a mold as shown in each of Comparative Examples 1 and 2 below. That is, Comparative Example 1 is one in which the test piece is injection-molded using a mold having the same main cavity as in the experimental example and omitting the movable mold part and the auxiliary cavity. Comparative Example 2 is one in which the test piece is injection-molded using a mold having the same main cavity as the experimental example and omitting only the movable mold part of the auxiliary cavity. [Dimension Setting of Test Piece] In these experimental examples, Comparative Examples 1 and 2, the dimensions of the test piece were set as follows. Thickness: 3 mm Length: 1000 mm Width: 100 mm [Injection conditions] Also, the above experimental examples, comparative examples 1, and
In Comparative Example 2, an 800-ton injection molding machine was used and injection molding was performed under the same injection conditions as described below. Injection conditions Materials used: Polypropylene (MI = 10) Molding temperature: 240 ° C Mold temperature: 30 ° C Filling time: 3. 0 seconds Gas injection pressure: 10 MPa (4.0 seconds)

[Experimental Result] In the experimental example, it was possible to obtain a non-defective product having no defective portion such as “sink” on the surface of the molded product. FIG. 7 shows a molded product 71 according to Comparative Example 1. Here, in the molded product 71, only the left side in the drawing is fractured to expose the internal gas channel 72, and the right side in the figure is shown in a state where the injection-molded surface is intact without being fractured. In Comparative Example 1, as shown in the figure, the injected high-pressure gas cannot proceed beyond the substantially central portion of the molded product 71, and the gas channel 72 forms only about half of the entire length of the molded product 71. I couldn't. Therefore, in the vicinity of the flow end position E without the gas channel 72, a defective portion 73 such as a sink mark or a warp was generated on the surface. FIG. 8 shows a molded product 83 according to Comparative Example 2. Where the molded article 83
Is entirely broken to expose the internal gas channels 81, 82. In Comparative Example 2, as shown in the figure,
The injected high-pressure gas forms upper and lower two gas channels 81 and 82 in the figure over the entire length of the molded product 83. However, in the lower gas channel 82 in the drawing, in the vicinity of the flow end position F, a blowout phenomenon occurs in which the high-pressure gas flows out of the molten resin 84. Due to this blowout phenomenon, the flow end position F of the molded product 83
In the vicinity of, since the inside was not hollow, a defective portion such as a sink occurred on the surface.

The present invention is not limited to the above-mentioned embodiments, but includes the following modifications. That is, the retreat control means is not limited to a planar spacer, but as shown in FIG. 9, a cam that is arranged behind the movable mold part 40 and has a cam 61 that can be fixed at an arbitrary rotational position. 10 or a screw type configured to include a bolt 62A capable of advancing and retracting with respect to the movable mold part 40 and a lock nut 62B for fixing the bolt 62A, as shown in FIG. If such a cam type or screw type is used, an effect that the rearmost position where the movable mold part can be retracted can be finely adjusted can be obtained. When using a cam type or screw type as the reverse control means,
Alternatively, it is preferable to dispose the driving means 63 in front of the movable mold section 40 (above the movable mold section 40 in the figure) so that the screw 62 and the driving means 63 do not interfere with each other.

The passive movable mold part is not limited to a conical head part, and a movable mold part 65 having a substantially flat head part 64 is adopted as shown in FIG. If such a movable mold part 65 is adopted, the upper surface 24A of the auxiliary cavity 24 in the upper part of the drawing is made to be a concave surface so that the gas pressure and the like are different between the upper surface 24A and the movable mold part 65. If it is transmitted between them, the movable mold part 65 can be retracted.

Further, the biasing means for the passive movable mold part is not limited to the coil spring 53 which can be obtained only by a constant biasing force in the closed position, and as shown in FIG. A coil spring 67 that can be compressed by tightening or an air spring such as an air cylinder device may be used, and if such biasing means is adopted, the biasing force can be finely adjusted.

Further, the biasing means of the passive movable mold part may be omitted, and when the biasing means is omitted, as shown in FIG. 12, it is possible to project and retract from the inner surface of the auxiliary cavity 24. The movable mold part 69 may be fixed at the closed position A and injection molding may be performed until the gas injection starts. Further, the driving means is not limited to a fluid pressure type such as a hydraulic cylinder device, but may be an electromagnetically operated type such as a motor or an electromagnet.

The gas injection timing may be any time after the start of filling, and may be before or after the completion of filling. Further, the auxiliary cavity is not limited to one provided on the outer cavity side of the main cavity, but may be provided on the core side of the mold when the gas channel passage end position is inside the main cavity. The installation position of the cavity may be appropriately set according to the shape of the molded product and the like.

Further, in the case of injection-molding a resin such as an engineer plastic, which solidifies quickly, an auxiliary cavity is used.
A temperature adjusting device such as an electric heater may be provided in the vicinity of 24. As the temperature adjusting device, in addition to an electric heater, a combustion type heater or a heater using high frequency can be adopted.

The pressurizing gas is not limited to nitrogen gas, but may be an inert gas such as argon, that is, any gas that can avoid the danger of explosion even at high pressure.

[0030]

As described above, according to the present invention, it is possible to reduce the load of manufacturing a mold and to mold a large-sized sheet product satisfactorily.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing the overall configuration of a first embodiment of the present invention.

FIG. 2 is a perspective view showing a main cavity and an auxiliary cavity of the embodiment.

FIG. 3 is an enlarged cross-sectional view showing a closed state of the auxiliary cavity of the embodiment.

FIG. 4 is an enlarged cross-sectional view showing an opened state of the auxiliary cavity of the embodiment.

FIG. 5 is a diagram corresponding to FIG. 3 showing a second embodiment of the present invention.

FIG. 6 is a view corresponding to FIG. 4 showing the same embodiment.

FIG. 7 is a partially cutaway plan view showing a comparative example.

FIG. 8 is a plan sectional view showing another comparative example.

FIG. 9 is a view corresponding to FIG. 3 showing a modification of the present invention.

FIG. 10 is a view corresponding to FIG. 3 showing another modification of the present invention.

FIG. 11 is a view corresponding to FIG. 3 showing a different modification of the present invention.

FIG. 12 is a diagram corresponding to FIG. 3 showing still another modified example of the present invention.

[Explanation of symbols]

 20 Mold 23 Main cavity 24 Auxiliary cavity 30 Molten resin 31,71,83 Molded product 32 Gas channel 40,50,65,69 Movable mold part 41 Hydraulic cylinder device as drive means 43, 54 Spacer as retreat control means 53, 67 Spring as biasing means 61 Cam as backward control means 62A Bolt as backward control means

Claims (7)

[Claims] 1. A method for injecting a pressurized gas into the main cavity after starting the filling of the molten resin into the main cavity of the mold to form a gas channel, which is a passage for the pressurized gas, inside the molten resin. While the method is a gas injection molding method for performing injection molding, a cylinder-shaped auxiliary cavity communicating with the main cavity is provided in the mold, and the inner volume of the auxiliary cavity is made variable, A gas characterized by expanding the internal volume of the movable mold part when injecting a pressurized gas into the main cavity after starting to fill the main cavity with a molten resin in a state where the internal volume is reduced. Injection molding method. 2. After starting to fill the main cavity with the molten resin, a pressurized gas is injected into the main cavity to form a gas channel as a passage for the pressurized gas inside the molten resin. A mold for gas injection molding that performs injection molding while a cylinder-shaped auxiliary cavity that communicates with the main cavity and a piston shape that advances and retreats inside the auxiliary cavity to change the internal volume of the auxiliary cavity. And a retreat control means for controlling the retreat of the movable die part to the rear from an arbitrary intermediate position. 3. The gas injection molding die according to claim 2, wherein the die is provided with an urging means, and the urging means urges the movable die part in the forward direction and injects it. A gas injection molding die characterized in that it can be retracted by the applied gas pressure. 4. The gas injection molding die according to claim 2, wherein the movable die part is connected to a driving means, and the driving means can advance and retreat in the auxiliary cavity. Injection mold. 5. The gas injection molding die according to claim 4, wherein the driving means is a hydraulic cylinder device. 6. The gas injection molding die according to claim 4, wherein the driving means is an electromagnetic actuating mechanism. 7. The gas injection molding die according to any one of claims 2 to 6, wherein the retreat control means is a spacer arranged behind the movable die connection. Gas injection mold.