JP5630476B2 - Injection molding method and injection molding apparatus - Google Patents

Description

  The present invention relates to an injection molding method and an injection molding apparatus capable of easily manufacturing a thick-walled or rod-shaped resin molded product with high dimensional accuracy.

  Conventionally, cutting, injection molding, or the like has been used as a method for producing various industrial products such as thick or rod-like products. Although cutting can obtain a highly accurate product, milling or the like is performed after molding with a raw material or a mold, so there are problems such as heavy equipment costs and poor productivity. In addition, manufacturing by injection molding can be used as an alternative to cutting because of the advantages of lighter product and improved productivity, but it is prone to sink due to solidification shrinkage, and it is not possible to obtain a highly accurate product There is.

  Therefore, in the injection molding technique, various improvements have been made in order to prevent sink marks generated on the surface of the molded product. For example, in Patent Document 1, a resin containing a foaming agent or the like is cooled and solidified in a mold, and a movable part of the mold is moved to generate a foamed part inside the molten resin, thereby preventing sink marks. (Core back) is disclosed. According to this method, the occurrence of sink marks can be suppressed even in a molded product that partially has a portion that causes a thickness deviation such as a protruding portion.

JP 2005-288745 A

  However, the scope of application of the improved technique described in the above-mentioned Patent Document 1 is narrow, especially when a thick-walled or rod-shaped resin molded product is manufactured by these techniques, there is no correction due to factors such as variations in molding shrinkage rate. Therefore, it is impossible to mold a resin product having a desired dimensional accuracy, and it is necessary to repeatedly perform a modification such as a molding test and mold rework.

  Accordingly, the present invention has been made in view of the problems in the prior art, and improves the dimensional accuracy of a resin molded product such as a thick wall and is easy to manufacture. An object is to provide an apparatus.

In order to solve the above problems, the present invention forms a generally thick cavity between a mold and a core, injects resin into the cavity, and fully fills the cavity with resin. After the resin is fully filled , the core is retracted to form a cavity again while maintaining the internal pressure of the cavity at a predetermined pressure or more, and the resin is injected into the re- formed cavity and molded. And In the injection molding method, the second and subsequent injection steps can be performed continuously.

  According to the present invention, the resin previously filled in the cavity solidifies sequentially from the surface in contact with the mold, and at the same time, new resin is continuously replenished under a predetermined pressure. The occurrence of sink marks due to contraction can be stably suppressed. Moreover, since these processes are performed until the final shape is formed, the dimensional accuracy of the resin molded product such as a thick wall is remarkably improved.

  Specifically, in contrast to the columnar design shape shown in FIG. 1 (a), in the conventional method, as shown in FIG. 1 (b), a plastic product has a large shrinkage rate at the time of solidification. Shrinkage deformation occurs toward the central portion, and in the case of a molded product such as a thick wall, the shrinkage becomes particularly obvious and a desired design shape cannot be obtained. On the other hand, according to the method of the present invention, as shown in FIG. 1 (c), high-precision molding is possible, and a molded product having the same design shape is obtained.

  Furthermore, since the resin is injected and the outer peripheral surface (die contact surface) is continuously formed, and the internal temperature is always higher than the surface resin temperature, and the reinforcing agent does not easily float on the surface layer. A stable resin skin layer can be obtained on the surface, and the appearance (surface roughness) can be improved as compared with molding in the conventional method.

  While maintaining the internal pressure of the cavity at a predetermined level, the resin can be injected and molded so that the core is retracted by a predetermined pressure control according to the pressure of the resin injected into the cavity. Thereby, a resin molded product with higher dimensional accuracy can be manufactured.

  A step of promoting foaming inside the resin containing the foaming agent by further retracting the core after the final injection step can be combined. As a result, the internal pressure of the cavity rapidly decreases, so that the foaming agent contained in the resin expands, and the desired design shape is obtained by offsetting shrinkage due to sink.

  A step of advancing the core after promoting foaming inside the resin may be combined. Thereby, when resin is pressurized, the excessive expansion | swelling by foaming is suppressed, and it becomes possible to raise a product density and to stabilize dimensional accuracy.

  In the above injection molding method, the core can be moved backward while being rotated so as to follow the mold whose interior is carved. Thereby, not only a simple cylindrical resin product but also a resin molded product having a complicated contour shape can be manufactured.

Further, the present invention is an injection molding apparatus, comprising: a mold having a gate portion; a core which is disposed so as to be fitted to the mold and can be contacted and separated from the gate portion; the mold; Means for injecting resin from the gate part into the cavity formed between the core, means for measuring the internal pressure of the cavity, and measured by the measuring means when the core is separated from the gate part. said comprising means for controlling the internal pressure of the cavity to a predetermined value or more, movement of the injection and the core of said resin is characterized Rukoto performed alternately with. According to the present invention, similarly to the above-described invention, the occurrence of sink marks due to shrinkage during solidification can be stably suppressed, and the dimensional accuracy of a resin molded product such as a thick wall can be remarkably improved.

  As described above, according to the present invention, it is possible to provide an injection molding method and an injection molding apparatus capable of easily manufacturing a thick-walled or rod-shaped resin molded product with high dimensional accuracy.

It is a comparison figure of the injection molding goods by the conventional method and the method of this invention. It is a schematic sectional drawing which shows 1st Embodiment of the injection molding apparatus concerning this invention. It is a figure which shows each process of the injection molding method concerning this invention. The meaning which is a flowchart which shows the injection molding method concerning this invention. It is a flowchart which shows the sub process 2 of the injection molding method concerning this invention. It is a flowchart which shows the sub process 3 of the injection molding method concerning this invention. It is a schematic sectional drawing which shows 2nd Embodiment of the injection molding apparatus concerning this invention. It is a flowchart which shows the injection molding method using the injection molding apparatus of FIG. It is a schematic sectional drawing which shows 3rd Embodiment of the injection molding apparatus concerning this invention. It is a flowchart which shows the injection molding method using the injection molding apparatus of FIG. It is a graph for demonstrating the conventional basic injection molding method. In this invention, it is a graph for demonstrating the method to manufacture a resin molded product with higher dimensional accuracy.

  Next, an embodiment for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 2 shows a first embodiment of an injection molding apparatus according to the present invention. The injection molding apparatus 1 is disposed so as to be fitted to a mold 2 having a gate portion 2a and the mold 2, Means for injecting resin from the gate part 2a into the cavity 3 formed between the mold 2 and the core 3; The load cell 5 that measures the internal pressure of the cavity 3 and the cylinder 6 that controls the movement of the core 3 so that the internal pressure value of the cavity 4 measured by the load cell 5 is not less than a predetermined value.

  Next, an injection molding method according to the present invention using the injection molding apparatus 1 will be described with reference to FIGS. In FIG. 3, only the mold 2 and the core 3 shown in FIG. 2 are shown, and other components are not shown.

  First, the mold 2 is clamped in step S1, and the core 3 is set in the cavity 4 in step S2 (state shown in FIG. 3A). When the setting of the core 3 is completed (step S3; Yes), the resin is injected from the gate portion 2a into the cavity 4 (step S4, FIG. 3B). In step S5, it is determined whether or not the internal pressure of the cavity 4 is equal to or higher than a set value. If it is equal to or higher than the set value (step S5; Yes), the core 3 starts to be retracted in step S6. At this time, the resin in the cavity 4 starts to solidify from the surface in contact with the mold 2 (state shown in FIG. 3C). On the other hand, when the internal pressure of the cavity 4 is lower than the set value in step S5 (step S5; No), the process returns to step S4 to inject resin into the cavity 4 from the gate portion 2a, and thereafter this operation is repeated.

  After retracting the core 3 in step S6, it is determined in step S7 whether or not the internal pressure of the cavity 4 is equal to or higher than a set value. If the pressure is equal to or higher than the set value (step S7; Yes), the core is determined in step S8. Stop 3 backwards. On the other hand, when the internal pressure of the cavity 4 is lower than the set value in step S7 (step S7; No), the process returns to step S4 to inject resin into the cavity 4 from the gate portion 2a, and thereafter this operation is repeated. Thereby, the resin in the cavity 4 continues to solidify the surface in contact with the mold 2, and the inside of the cavity 4 is melted from the gate portion 2 a, and the injection is continued while the core 3 is retracted ( FIG. 3 (d) state).

  After stopping the retreat of the core 3 in step S8, it is determined in step S9 whether or not the internal pressure of the cavity 4 is equal to or higher than the set value. If it is equal to or higher than the set value (step S9; Yes), in step S10. It is determined whether or not the core 3 is at the stop position, and if it is the stop position (step S10; Yes), the movement of the core 3 is stopped and the injection is completed (state shown in FIG. 3E). Thereafter, the process proceeds to sub-process 2 as necessary in step S11. On the other hand, if the internal pressure of the cavity 4 is lower than the set value in step S9 (step S9; No), the process returns to step S4, and if not the stop position of the core 3 in step S10 (step S10; No). Returning to step S4, the operation is subsequently repeated a plurality of times.

  As described above, the resin injected into the cavity 4 is solidified sequentially from the surface in contact with the mold 2 and at the same time, new resin is continuously replenished under a predetermined pressure. Can be stably suppressed, and this state is performed until the final shape is formed, so that it is possible to obtain a cylindrical resin molded product with significantly improved dimensional accuracy.

  Next, the sub process 2 will be described with reference to FIGS. This step can be performed when a foaming agent is contained in the resin.

  From the state of FIG. 3 (e), in step S21, the core 3 is retracted at a high speed (state of FIG. 3 (f)), and in step S22, it is determined whether or not the core 3 is at the stop position. When it is in the stop position (step S22; Yes), the backward movement of the core 3 is stopped, and thereafter, the process proceeds to the sub-process 3 as necessary in step S23. On the other hand, when the core 3 is not in the stop position in step S22 (step S22; No), the core 3 is continuously retracted until it reaches the stop position. By the high-speed retreat of the core 3, foaming is promoted inside the resin in the cavity 4, the resin expands, and the desired design shape can be obtained by offsetting the shrinkage of the resin due to sink.

  Next, the sub process 3 will be described with reference to FIGS.

  From the state of FIG. 3 (f), in step S31, the core 3 is advanced by a small amount at a high speed (state of FIG. 3 (g)), and in step S32, it is determined whether or not the core 3 is at the stop position. If it is at the stop position (step S32; Yes), the advance of the core 3 is stopped and the process is terminated. On the other hand, if the core 3 is not in the stop position in step S32 (step S32; No), the core 3 continues to advance until it reaches the stop position. By the high-speed micro advance of the core 3, the resin inside the cavity 4 is pressurized, excessive expansion due to foaming is suppressed, the product density can be increased, and the dimensional accuracy can be stabilized.

  In the above embodiment, the case where a cylindrical resin molded product is manufactured has been described. However, a desired shape is engraved inside the mold 2 so that the core 3 follows the inner surface of the mold 2. By performing each of the above steps while rotating, it is possible to manufacture not only a cylindrical resin product but also a resin molded product having a complicated contour shape having a spiral portion such as a screw.

  Next, a second embodiment of the injection molding apparatus according to the present invention will be described with reference to FIGS.

  The injection molding apparatus 11 includes a mold 12 having a gate portion 12a, a core 13 that is disposed so as to be fitted to the mold 12 and that can move in a direction in which the gate portion 12a is contacted and separated, and a mold 12 A means (not shown) for injecting resin from the gate portion 12a to the cavity 14 formed between the core 13; a measuring means (not shown) for measuring the internal pressure of the cavity 14; and a cavity measured by the measuring means. The air cylinder 15 controls the movement of the core 13 via the support portion 16 by a servo mechanism so that the internal pressure of 14 becomes a predetermined value, the detection portion 18 fixed to the support portion 16, and the frame 17 It consists of two limit switches 19, 20 and the like.

  Next, an injection molding method according to the present invention using the injection molding apparatus 11 will be described with reference to FIGS.

  First, the mold 12 is clamped in step S41, and the core 13 is set in the cavity 14 in step S42. When the limit switch 19 is turned on by the detection unit 18 (step S43; Yes), resin is injected from the gate unit 12a into the cavity 14 (step S44). In step S45, it is determined whether or not the internal pressure of the cavity 14 is equal to or higher than a set value. If it is equal to or higher than the set value (step S45; Yes), the core 13 starts to be retracted in step S46. At this time, the resin in the cavity 14 starts to solidify from the surface in contact with the mold 12. On the other hand, when the internal pressure of the cavity 14 is lower than the set value in step S45 (step S45; No), the process returns to step S44 to inject resin into the cavity 14 from the gate portion 12a, and thereafter this operation is repeated.

  After retracting the core 13 in step S46, it is determined in step S47 whether or not the internal pressure of the cavity 14 is equal to or higher than the set value. If the pressure is higher than the set value (step S47; Yes), the core is determined in step S48. Stop 13 backwards. On the other hand, when the internal pressure of the cavity 14 is lower than the set value in step S47 (step S47; No), the process returns to step S44 to inject resin into the cavity 14 from the gate portion 12a, and thereafter this operation is repeated. Thereby, the resin in the cavity 14 continues to solidify the surface in contact with the mold 12, and the inside of the cavity 14 is melted from the gate portion 12 a, and the injection is continued while the core 13 is retracted.

  After stopping the retreat of the core 13 in step S48, it is determined in step S49 whether or not the internal pressure of the cavity 14 is equal to or higher than a set value. If it is equal to or higher than the set value (step S49; Yes), in step S50. The detection unit 18 determines whether or not the limit switch 20 is turned on. When the limit switch 20 is turned on (step S50; Yes), the movement of the core 13 is stopped and the injection is completed. Thereafter, the process proceeds to the sub-process 2 shown in FIG. On the other hand, if the internal pressure of the cavity 14 is lower than the set value in step S49 (step S49; No), the process returns to step S44, and if the limit switch 20 is not turned on in step S50 (step S50; No). In addition, the process returns to step S44, and thereafter this operation is continuously repeated a plurality of times.

  As described above, the resin injected into the cavity 14 is sequentially solidified from the surface in contact with the mold 12, and at the same time, new resin is continuously replenished under a predetermined pressure. Can be stably suppressed, and this state is performed until the final shape is formed, so that it is possible to obtain a cylindrical resin molded product with significantly improved dimensional accuracy.

  Next, a third embodiment of the injection molding apparatus according to the present invention will be described with reference to FIGS.

  The injection molding apparatus 31 includes a mold 32 having a gate portion 32a, a core 33 that is disposed so as to be fitted to the mold 32, and that can move in the direction of contact with and away from the gate portion 32a, and the mold 32. A means (not shown) for injecting resin from the gate portion 32a into the cavity 34 formed between the core 33, a measuring means (not shown) for measuring the internal pressure of the cavity 34, and a cavity measured by the measuring means The air cylinder 35 that controls the movement of the core 33 via the support portion 36 by a servo mechanism so that the internal pressure of the air pipe 34 becomes a predetermined value, and is fixed to the air cylinder 35 and detects the approach of the piston 35a of the air cylinder 35. It consists of two proximity switches 39, 40, etc.

  Next, an injection molding method according to the present invention using the injection molding apparatus 31 will be described with reference to FIGS.

  First, the mold 32 is clamped in step S61, and the core 33 is set in the cavity 34 in step S62. When the piston 35a of the air cylinder 35 approaches the proximity switch 39 and the proximity switch 39 is turned on (step S63; Yes), the resin is injected from the gate portion 32a into the cavity 34 (step S64). In step S65, it is determined whether or not the internal pressure of the cavity 34 is equal to or higher than the set value. If it is equal to or higher than the set value (step S65; Yes), the core 33 starts to be retracted in step S66. At this time, the resin in the cavity 34 starts to solidify from the surface in contact with the mold 32. On the other hand, when the internal pressure of the cavity 34 is lower than the set value in step S65 (step S65; No), the process returns to step S64 to inject resin into the cavity 34 from the gate portion 32a, and this operation is repeated thereafter.

  After retreating the core 33 in step S66, it is determined in step S67 whether or not the internal pressure of the cavity 34 is equal to or higher than the set value. If it is equal to or higher than the set value (step S67; Yes), the core is determined in step S68. Stop the 33 backwards. On the other hand, when the internal pressure of the cavity 34 is lower than the set value in step S67 (step S67; No), the process returns to step S64 to inject resin from the gate portion 32a into the cavity 34, and thereafter this operation is repeated. As a result, the resin in the cavity 34 continues to solidify the surface in contact with the mold 32, and the inside of the cavity 34 is melted from the gate portion 32 a, and the injection is continued while the core 33 is retracted.

  After stopping the retreat of the core 33 in step S68, it is determined in step S69 whether or not the internal pressure of the cavity 34 is equal to or higher than the set value. If it is equal to or higher than the set value (step S69; Yes), in step S70. It is determined whether the piston 35a of the air cylinder 35 approaches the proximity switch 39 and the proximity switch 40 is turned on. When the proximity switch 40 is turned on (step S70; Yes), the movement of the core 33 is stopped and injection is performed. Complete. Thereafter, the process proceeds to the sub-process 2 shown in FIG. On the other hand, if the internal pressure of the cavity 34 is lower than the set value in step S69 (step S69; No), the process returns to step S64, and if the proximity switch 40 is not turned on in step S70 (step S70; No). In addition, the process returns to step S64, and this operation is subsequently repeated a plurality of times.

  As described above, the resin injected into the cavity 34 is sequentially solidified from the surface in contact with the mold 32, and at the same time, new resin is continuously replenished under a predetermined pressure. Can be stably suppressed, and this state is performed until the final shape is formed, so that it is possible to obtain a cylindrical resin molded product with significantly improved dimensional accuracy.

  In the above embodiment, the movement of the core 33 is controlled by the air cylinder 35, but it can also be controlled by a hydraulic cylinder / servo motor or the like.

  Next, in the injection molding method according to the present invention, a method for producing a resin molded product with higher dimensional accuracy will be described in comparison with a conventional injection molding method.

  First, a conventional basic injection molding method will be described with reference to FIG. In FIG. 11, the horizontal axis represents the time elapsed from the start of injection molding, and the vertical axis represents the molding pressure of the injection molding machine.

The conventional method is as follows.
(1) The plastic synthetic resin put into the injection molding machine is melted with a cylindrical heating cylinder.
(2) At the same time, the synthetic resin is uniformly plasticized by rotating a screw installed in the cylinder.
(3) The molten synthetic resin collected forward by the rotation of the screw is injected at high pressure and high speed with the screw directed forward, and the molten synthetic resin is fed into the mold.
(4) The injection (holding pressure) process is roughly divided into the following three stages.
(a) As a primary stage, injection is performed with a capacity (injection pressure / speed) of 80 to 90% of the capacity of the injection molding machine.
(b) As a secondary stage, injection is performed with a capacity of 20 to 40% of the capacity of the injection molding machine.
(c) As the third stage, injection is performed with a capacity of 10 to 30% of the capacity of the injection molding machine.
(5) The molded product is cooled during the pressure-holding step, and after a certain period of time, the product and its accessories are taken out.

  In the above-described conventional injection molding method, the quality of the product (dimensional accuracy) depends on the numerical values relating to the capabilities of (4) (a) to (c) and by further subdivided multistage control.

  Next, in the injection molding method according to the present invention, a method for producing a resin molded product with higher dimensional accuracy will be described.

First, the synthetic resin is fed into the mold by the same steps as the conventional steps (1) to (3), and then
(4) The injection / holding process is performed in one stage (one condition). That is, in a state where the capacity (injection pressure / speed) of the injection molding machine is kept constant (for example, 90% of the capacity), the synthetic resin is fed into the cavity until the volume of the cavity is filled (see FIG. 12). ). At this time, the core is retracted at a constant speed by the pressure of the resin injected into the cavity. That is, the cavity volume change rate is controlled to be constant, and the cavity volume is changed in an increasing direction from the start to the end of the injection / holding process.

  In the present invention, the quality of the product (dimensional accuracy) is controlled by the pressure in the cavity and the volume change rate of the cavity. In addition, as an auxiliary means, it can be made to foam inside the molded product to further improve the quality.

  The pressure in the cavity is 2 MPa to 5 MPa. For example, when the volume of the cavity is 50 cc, the cavity volume changing speed is set so that the moving distance 38 mm moves in 0.5 seconds to 3 seconds. . Here, there is a correlation between the pressure in the cavity and the volume change rate of the cavity, and these relations differ depending on the volume of the cavity.

  The pressure in the cavity is controlled for the purpose of controlling the foaming phenomenon, but the pressure in the cavity changes depending on the characteristics of the foaming agent, so it is necessary to change the pressure setting value according to the type of foaming agent used. is there.

DESCRIPTION OF SYMBOLS 1 Injection molding apparatus 2 Mold 2a Gate part 3 Core 4 Cavity 5 Load cell 6 Cylinder 11 Injection molding apparatus 12 Mold 12a Gate part 13 Core 14 Cavity 15 Air cylinder 16 Support part 17 Frame 18 Detection part 19, 20 Limit switch 31 Injection Molding device 32 Mold 32a Gate part 33 Core 34 Cavity 35 Air cylinder 35a Piston 36 Support part 39, 40 Proximity switch

Claims (7)

Forming a cavity between the mold and the core,
Injecting resin into the cavity to fully fill the cavity with the resin,
After full filling of the resin, while maintaining the internal pressure of the cavity above a predetermined pressure, the core is retracted to form a cavity again ,
An injection molding method comprising molding a resin by injecting a resin into the re-formed cavity .   The injection molding method according to claim 1, wherein the second and subsequent injection steps are continuously performed.   The resin is injected and molded so that the core is moved backward by a predetermined pressure control according to the pressure of the resin injected into the cavity while maintaining the internal pressure of the cavity at a predetermined level. Item 3. The injection molding method according to Item 1 or 2.   4. The injection molding method according to claim 1, wherein foaming inside a resin containing a foaming agent is promoted by further retracting the core after the last injection step. 5.   The injection molding method according to claim 4, wherein after the foaming inside the resin is promoted, the core is advanced.   The injection molding method according to claim 1, wherein the core is retreated while being rotated so as to follow the mold whose interior is carved. A mold having a gate part;
A core disposed so as to be fitted to the mold and capable of contacting and separating from the gate portion;
Means for injecting resin from the gate portion into a cavity formed between the mold and the core;
Means for measuring the internal pressure of the cavity;
Means for controlling the internal pressure of the cavity measured by the measuring means to a predetermined value or more when the core is separated from the gate portion ;
Injection molding apparatus move the injection and the core of said resin is characterized Rukoto alternately performed.

Images