JP2007083685A - Injection molding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique capable of reducing not only the peak value of in-mold pressure acting on an injection mold but also the durable pressure required in the injection mold. <P>SOLUTION: The injection molding method comprises a process for applying mold clamping force to a mold 2 to close the mold 2, a filling process for filling the cavity 2a of the mold 2 with a molten resin in a state that the mold clamping force is applied to the mold 2, a cooling process for cooling the molten resin charged in the mold 2, and a process for opening the cavity 2a to eject an injection-molded product 40 from the mold 2. The mold clamping force applied to the mold 2 in the fitting process is set lower than that necessary for holding the mold 2 to a perfectly closed state against the filling pressure of the molten resin. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an injection molding technique for molding an injection molded product.

The injection molding method includes a step of closing the injection mold by applying a clamping force to the injection mold, a step of filling the cavity in the injection mold with a molten resin in a state where the clamping force is applied to the injection mold, and A step of cooling the molten resin filled in the cavity, and a step of opening the injection mold and taking out the injection-molded product from the injection mold.
In the step of filling the cavity with the molten resin, the cavity is filled with the molten resin by applying pressure to the molten resin. The filling pressure of the molten resin is a force for opening the injection mold. In order to prevent the injection mold from opening due to the filling pressure of the molten resin, the molten resin is filled into the cavity in the injection mold with a clamping force applied to the injection mold.
The mold clamping force required to maintain the injection mold in a completely closed state is determined by the mold internal pressure generated due to the filling pressure of the molten resin. The internal pressure of the mold (the pressure acting on the cavity surface that defines the cavity) varies with position. The injection mold is completely closed against the filling pressure of the molten resin by integrating the partial pressure of the mold internal pressure in the direction in which the mold can be opened over the area projected from the cavity surface in the mold clamping direction. It is possible to calculate the clamping force required to maintain the state of being in the state.
In the conventional technology, in a state where a clamping force larger than the clamping force necessary for maintaining the injection mold in a completely closed state against the filling pressure of the molten resin is applied to the injection mold, Perform the filling process.
In addition, when injection molding a thin-walled product, it is necessary to fill a cavity with a narrow interval with a molten resin. A high filling pressure is required to fill the cavity with a narrow interval with the molten resin. Since the filling pressure is high, the clamping force required to keep the injection mold closed against it increases. When thin-walled products are injection-molded, a high-strength injection mold that can withstand a high filling pressure and a large mold-clamping mechanism that closes the mold are required.

When the cavity is filled with the molten resin, the molten resin is then cooled and solidified. The molten resin shrinks as it solidifies. Without countermeasures against shrinkage, the solidified injection-molded product does not match the cavity shape. A “shrink” that contracts more than the cavity shape occurs. Therefore, a pressure holding step is required in which pressure is continuously applied to the molten resin filling the cavity even after the cavity is filled with the molten resin. When the pressure holding step is performed, the molten resin is additionally filled so as to supplement the shrinkage of the molten resin in the cavity, and it is possible to prevent occurrence of “sinking” in the injection molded product.
The injection mold requires a strength that can withstand the pressure applied in the pressure-holding step and a clamping force that closes the injection mold in the pressure-holding step.

FIG. 9 shows how the clamping force required to be applied to the injection mold and the pressure acting on the cavity surface (in-mold pressure) change. The in-mold pressure reaches a peak at the end of the filling process and is managed at a certain level during the pressure holding process.
The mold internal pressure in FIG. 9 indicates the pressure acting on the cavity surface at a position facing the gate filled with the molten resin. Although the peak value is reached at the end of the filling process, the range in which the mold internal pressure is high is limited to the vicinity of the position facing the gate. The clamping force that closes the injection mold does not peak. In the pressure holding process, a pressure lower than the peak pressure at the end of the filling process acts, but the pressure is applied to a wide range of the cavity surface. Therefore, for a while after the pressure-holding step is started, the mold clamping force required to keep the injection mold closed is increased.

In the technique disclosed in Patent Document 1, the pressure holding step that is required after the step of filling the molten resin is omitted. In this technology, when the molten resin filling process is completed, instead of performing the pressure holding process, a pressure is applied between the back surface of the injection molded product and the cavity surface through a flow path that opens the back surface of the injection molded product. A pressurized fluid is injected to pressurize the injection-molded product toward the surface (design surface) side cavity surface. When the state where the back surface of the injection molded product is peeled off from the cavity surface is created, the design surface of the injection molded product maintains a state of being in close contact with the cavity surface even when the molten resin contracts. When the design surface of the injection-molded product is cooled in a state of being in close contact with the cavity surface, the design surface of the injection-molded product can be finished in the intended shape. According to this technique, it is possible to finish the design surface of an injection molded product into an intended shape. However, in this technique, it is necessary to apply a high pressure to the fluid injected between the back surface of the injection molded product and the cavity surface, and it is necessary to reduce the pressure applied to the cavity surface and keep the injection mold closed. The clamping force cannot be reduced.
Patent Document 2 discloses an injection molding technique that can finish the design surface of an injection molded product into an intended shape, and reduces the pressure applied to the cavity surface and requires a clamping force necessary to keep the injection mold closed. An injection molding technique capable of reducing the above is disclosed. It should be noted that the technique of Patent Document 2 is not yet published at the time of filing of the present application.
In this technique, after the step of filling the molten resin is completed, the pressure holding step and the step of injecting the pressurized fluid between the back surface and the cavity surface of the injection molded product are performed simultaneously. When the pressure holding process and the pressurized fluid injection process are performed at the same time, the holding pressure necessary to finish the design surface of the injection molded product into the intended shape (pressure applied to the molten resin that is additionally replenished to the cavity) and the injection molded product The pressure applied to the fluid injected between the back surface and the cavity surface can be reduced. According to the technique of Patent Document 2, the pressure applied to the cavity surface can be reduced (both the holding pressure applied to the molten resin and the pressure applied to the fluid act on the cavity surface, but can still be reduced) and injection The clamping force required to keep the mold closed can be reduced.
FIG. 10 shows the state of the clamping force required to be added to the injection mold and the change in the pressure acting on the cavity surface when the technique of Patent Document 2 is used. The pressure applied to the molten resin that is additionally replenished to the cavity in the pressure-holding step can be reduced, and the mold clamping force required during the pressure-holding step can be reduced.
Japanese Patent Laid-Open No. 10-58493 Description and drawing of Japanese Patent Application No. 2004-373751

With the technique of Patent Document 2, it is possible to reduce the pressure applied to the molten resin that is additionally replenished to the cavity in the pressure holding process, and it is possible to reduce the clamping force required in the pressure holding process. As shown in FIG. 10, the maximum value of the required clamping force has been successfully reduced from the maximum value required in the prior art.
However, even the technique of Patent Document 2 cannot reduce the peak value of the pressure acting on the cavity surface. The peak value of the pressure acting on the cavity surface is the value at the end of the filling process. In the technique of Patent Document 2, although the in-mold pressure required in the pressure holding process can be reduced, the peak value of the in-mold pressure acting at the end of the filling process cannot be reduced.
The injection mold must have a strength that can withstand the peak value of the internal pressure of the mold. If the peak value cannot be reduced, the pressure resistance required for the injection mold cannot be reduced. The mold cannot be downsized.
The present invention has been devised to solve the above problems. An object of the present invention is to provide a technique capable of reducing the peak value of the in-mold pressure acting on the injection mold and reducing the pressure resistance required for the injection mold.

(Invention of Claim 1)
In the injection molding method of the present invention, a mold clamping force is applied to the injection mold and the injection mold is closed, and the cavity in the injection mold is filled with a molten resin while the mold clamping force is applied to the injection mold. A step, a step of cooling the molten resin filled in the cavity, and a step of opening the injection mold and taking out the injection-molded product from the injection mold. The mold clamping force applied to the injection mold in the filling process is set lower than the mold clamping force required to keep the injection mold completely closed against the filling pressure of the molten resin.
The mold clamping force required to maintain the injection mold in a completely closed state may be obtained by calculation. Mold required to maintain the injection mold completely closed by integrating the partial pressure in the mold opening direction over the area projected from the cavity surface in the mold clamping direction. The fastening force can be calculated. Or you may obtain | require by experimenting.

In the injection molding method of the present invention, the clamping force applied to the injection mold in the filling process is lower than the clamping force required to keep the injection mold completely closed against the filling pressure. . For this reason, in the filling process, the injection mold is slightly opened by the filling pressure of the molten resin.
As described above, a high filling pressure is required to fill the molten resin into the cavity having a narrow interval. In other words, if the gap between the cavities is wide, the filling pressure required to fill the cavities decreases. In the present invention, this phenomenon is used to lower the filling pressure. If the injection mold is slightly opened in the filling process, the space between the cavities is widened. As a result, the filling pressure required for filling the cavity can be reduced.
According to the injection molding method of the present invention, the filling pressure can be reduced. Therefore, the mold internal pressure acting on the cavity surface can be reduced, and the peak value of the mold internal pressure generated at the end of the filling process can be reduced. Thereby, the pressure resistance required for the injection mold can be reduced, and the strength required for the injection mold can be reduced. And an injection mold can be reduced in size and the production cost of an injection mold can be reduced. As a result, the production cost of the injection-molded product can be reduced.

(Invention of Claim 2)
The clamping force applied to the injection mold in the filling step is preferably set to a force that opens the injection mold by an interval that does not cause burrs in the injection molded product due to the filling pressure of the molten resin.
The interval at which no burrs are generated varies depending on the filling pressure, the characteristics of the resin, the temperature of the injection mold, and the like. It can be obtained by experiment.
According to the injection molding method of the present invention, the required filling pressure can be reduced by widening the gap between the cavities within a range where no burrs are generated in the injection molded product. Thereby, a good-quality injection-molded product can be molded with a simple injection mold.

(Invention of Claim 3)
The clamping force applied to the injection mold in the filling step is preferably set to a force that opens the injection mold by 0.1 to 0.15 mm in the filling step.
Generally, when the injection mold is opened more than 0.15 mm, burrs are easily generated in the injection molded product. Even if the injection mold is opened, if the interval is 0.15 mm or less, the molten resin does not enter the interval. It has been confirmed that burrs are unlikely to occur in injection molded products. In this case, the amount of opening of the mold becomes 0 as the process proceeds and the pressure in the mold decreases, and it has been confirmed that even if the injection mold is opened during filling, the thickness of the injection molded product is not affected.
In general, when the injection mold is opened by 0.1 mm or more, a phenomenon in which the filling pressure necessary for filling the cavity is decreased due to an increase in the space between the cavities becomes remarkable.
Therefore, the clamping force applied to the injection mold in the filling process is preferably set to a force that opens the injection mold by 0.1 to 0.15 mm in the filling process.

(Invention of Claim 4)
Following the filling step, it is preferable to carry out a pressure-holding step of continuously filling the cavity with the molten resin by continuously applying pressure to the molten resin filling the cavity with a clamping force applied to the injection mold.
If the injection molding method of this invention is used, the part which molten resin shrunk in the cavity can be replenished. Thereby, sink marks and voids can be prevented from occurring in the injection molded product.

(Invention of Claim 5)
When the injection mold includes a mold that molds the design surface of the injection molded product and a mold that molds the back surface of the injection molded product, a pressurized fluid is placed between the mold that molds the back surface and the resin filled in the cavity. It is preferable to carry out an injection step of injecting.
According to the injection molding method of the present invention, the surface (design surface) of the injection-molded product keeps in close contact with the cavity surface even when the molten resin contracts. Thereby, the design surface of an injection-molded product can be finished in the intended shape.

(Invention of Claim 6)
If the injection mold has a mold that molds the design surface of the injection-molded product and a mold that molds the back surface of the injection-molded product, the clamping force is applied to the injection mold following the filling process. Both the pressure-holding process that continues to apply pressure to the molten resin that fills the cavity and additionally fills the cavity with the molten resin, and the injection process that injects pressurized fluid between the mold that molds the back surface and the resin that fills the cavity It is preferable to carry out at the same time.
By carrying out the step of injecting the pressurized fluid, the holding pressure required in the pressure holding step can be reduced. By performing the pressure holding step, the pressure of the fluid to be injected toward the back surface of the injection molded product can be reduced. In the step of filling the molten resin, the filling pressure can be reduced by widening the gap between the cavities. These are comprehensively combined, and the peak value of pressure (in-mold pressure) applied to the cavity surface can be reduced, and the maximum value of the clamping force applied to the injection mold can be reduced.
The strength required for the injection mold can be reduced, and the injection mold can be reduced in size. In addition, the clamping force can be reduced, and the clamping mechanism can be reduced in size. The injection molding apparatus can be downsized.

  According to the present invention, the filling pressure of the molten resin can be reduced, and the peak value of the pressure applied to the cavity surface (in-mold pressure) can be reduced. The strength required for the injection mold can be reduced, and the injection mold can be reduced in size. This reduces the production cost of the injection mold. In addition, the replacement operation of the injection mold is facilitated.

The main features of the embodiments described below are listed.
(First form)
The injection-molded product mold is set so that it is opened by 0.1 to 0.15 mm in the filling process and is completely closed at the end of the pressure-holding process.

An embodiment according to the injection molding method of the present invention will be described with reference to FIGS. In this embodiment, an automobile bumper is injection molded by the injection molding method of the present invention.
FIG. 1 shows a state of the injection molding apparatus 1 used in the present embodiment before the mold 2 is closed. FIG. 2 shows a state in which the mold 2 of the injection molding apparatus 1 is closed and the injection cylinder 30 for injecting the molten resin is brought into contact with the molten resin injection gate 12a of the fixed mold 12. FIG. 3 shows a state in which molten resin is injected from the injection cylinder 30 into the cavity 2 a secured by closing the mold 2. FIG. 4 shows a state where the mold 2 is opened and the injection molded product 40 is taken out. FIG. 5 is a view for explaining an apparatus 50 for injecting pressurized air into the back side of the resin filled in the cavity 2a. FIG. 6 shows a process chart of the injection molding method of this embodiment. FIG. 7 is a diagram illustrating the relationship between the mold clamping force and the actual mold internal pressure. FIG. 8 shows the result of experiments confirming that the pressure at which the molten resin is injected may be smaller as the thickness of the injection molded product 40 (dimension in the mold clamping direction) is larger.

As shown in FIG. 1, the injection molding apparatus 1 is provided with a base 3, a fixed side device 10 disposed on the base 3, a movable side device 20, and an injection cylinder 30 for injecting molten resin. An injection device (not shown) is provided.
The stationary apparatus 10 is provided with a stationary platen 11. The stationary platen 11 is fixed vertically with respect to the base 3 arranged horizontally. The stationary platen 11 has a recess 11a on the injection cylinder side (the right side shown in FIG. 1). In the center of the recess of the recess 11a, a molten resin supply port 11b is provided at a portion where the nozzle head 31 of the injection cylinder 30 abuts. A fixed mold 12 is attached to the opposite side (left side shown in FIG. 1) of the recess 11a. The fixed mold 12 is provided with a gate 12 a to which molten resin is supplied from the injection cylinder 30. The fixed mold 12 is attached so that the opening on one side of the gate 12a communicates with the molten resin supply port 11b of the fixed platen 11 described above.
Further, the fixed platen 11 is provided with holes 13b to 16b penetrating in the thickness direction (the left-right direction shown in FIG. 1). Piston shafts 43 to 46 are inserted into the holes. The diameters of the piston shafts 43 to 46 are smaller than the diameters of the holes 13b to 16b. Therefore, the piston shafts 43 to 46 are configured to be movable in the left-right direction shown in FIG. 1 with respect to the stationary platen 11. Clamping cylinders 13 to 16 are attached to the injection cylinder 30 side of the holes 13 b to 16 b of the fixed side platen 11. One ends of the piston shafts 43 to 46 are accommodated in the cylinders 13 a to 16 a of the mold clamping cylinders 13 to 16.

  A movable platen 21 is provided in the movable device 20. The movable platen 21 is disposed vertically with respect to the base 3 disposed horizontally. The movable platen 21 is arranged so as to be slidable in the left-right direction shown in FIG. A piston shaft 17 a of a mold closing cylinder 17 is connected to the movable platen 21. A movable mold 22 is attached to the movable platen 21 on the fixed platen 11 side (the right side shown in FIG. 1). The movable platen 21 is provided with holes 23b to 26b penetrating in the thickness direction (left and right direction shown in FIG. 1). A thread is provided on the inner peripheral surface of each hole. Screw holes provided at the ends of the piston shafts 43 to 46 of the clamping cylinders 13 to 16 are screwed into the holes. The piston shafts 43 to 46 are fixed to the movable platen 21 by half nuts 23c to 26c, respectively.

  The injection cylinder 30 is supported by an injection device (not shown) so as to be slidable in the left-right direction shown in FIG. The injection cylinder 30 is provided with a nozzle head portion 31 that comes into contact with the concave portion 11 a of the stationary platen 11. The hollow portion 32 of the injection cylinder 30 is provided with a screw 33 that can slide in the hollow portion 32. In the hollow portion 32, molten resin is stored. Then, when the screw 33 of the hollow portion 32 slides leftward as shown in FIG. 1, the molten resin passes through the nozzle head 31 and the molten resin supply port 11 b provided in the concave portion 11 a, and the gate 12 a of the fixed mold 12. It is configured to be able to inject.

  Although omitted in FIG. 1, the movable mold 22 is provided with a flow path 27 and a flow path 28 as shown in FIG. The flow paths 27 and 28 have one end opened to the second cavity surface 22b and the other end opened to the outside. Vent members 27a and 28a are inserted into the openings of the flow paths 27 and 28, respectively. The vent members 27a and 28a are configured so that the molten resin does not enter the flow paths 27 and 28 when the cavity 2a is filled with the molten resin.

A pressurized air injection device 50 is connected to the flow paths 27 and 28. The pressurized air injection device 50 is provided with a filter 51, a regulator 52, and a valve 53. The filter 51, the regulator 52, and the valve 53 are interposed in the fluid pipe 54 in the order of the filter 51, the regulator 52, and the valve 53 from the one end 54 a side of the fluid pipe 54. The fluid pipe 54 connected to the outlet side of the valve 53 is bifurcated. One is connected to the flow path 27 and the other is connected to the flow path 28.
Note that high-pressure factory air is supplied to one end 54 a of the fluid pipe 54.
When the valve 53 of the pressurized air injection device 50 is opened, foreign matters are removed by the filter 51, and air whose pressure is regulated to a predetermined value (for example, 0.5 MPa) by the regulator 52 is supplied to the flow paths 27 and 28. Is done.

Each step of molding the injection molded product 40 using the injection molding apparatus 1 configured as described above will be described with reference to FIG.
When molding the injection molded product 40, first, a step of closing the molding die 2 is executed (refer to FIG. 2 together). The mold closing cylinder 17 is driven by a control device (not shown) of the injection molding apparatus 1, and the piston shaft 17a is driven rightward as shown in FIG. As a result, the movable platen 21 fixed to the piston shaft 17a slides in the right direction shown in FIG. The movable mold 22 attached to the movable platen 21 moves in the direction of the fixed mold 12, and the movable mold 22 and the fixed mold 12 are combined. That is, the mold 2 is in a closed state. In the state where the mold 2 is closed, the cavity 2 a is formed by the first cavity surface 12 b of the fixed mold 12 and the second cavity surface 22 b of the movable mold 22. The shape of the cavity 2a corresponds to that of the injection molded product 40 (refer to FIG. 4 together). The first cavity surface 12 b of the fixed mold 12 molds the design surface of the injection molded product 40. The second cavity surface 22b of the movable mold 22 forms the back surface and the end surface of the injection molded product 40. The design surface of the injection molded product 40 is a surface that needs to be finished to the intended surface shape. The back surface is a surface where the surface shape is not important. The time at which this mold closing process is started is assumed to be time t0 shown in FIG.

When the mold closing process is completed at time t1 shown in FIG. 6, a molten resin filling process is subsequently executed (refer to FIG. 3 together). In the filling process, since the internal pressure of the cavity 2a is increased by injecting the molten resin, the molten resin is injected into the cavity 2a while the mold 2 is clamped using the mold clamping cylinders 13, 14, 15, and 16. Details of the clamping force in the filling step will be described later. When the filling process is executed, the molten resin injected from the injection cylinder 30 passes through the gate 12a and is filled into the cavity 2a.
Then, at the timing (time t2 shown in FIG. 6) immediately after the molten resin passes through the vent members 27a and 28a provided in the flow paths 27 and 28, the pressurized air injection device 50 (see also FIG. 5). Valve 53 is opened. Thereby, an air injection process in which pressurized air is supplied to the flow paths 27 and 28 is started. The air supplied to the flow paths 27 and 28 is injected into the cavity 2a. Since the flow paths 27 and 28 are provided on the second cavity surface 22b side, the resin filled in the cavity 2a is peeled off from the second cavity surface 22b and is in close contact with the first cavity surface 12b. At this time, a gap is formed between the filled resin and the second cavity surface 22b. At the same time, the resin filled in the cavity 2a starts to shrink as the temperature decreases.

When the filling process is completed at time t3 shown in FIG. 6, the pressure holding process and the cooling process are started. In the pressure-holding step, the pressure applied from the gate 12a to the cavity 2a is maintained substantially constant, and the molten resin contracted by the cavity 2a is replenished. In the pressure-holding step, the internal pressure of the cavity 2a is increased by replenishing the molten resin. Therefore, the molten resin is replenished while the mold 2 is clamped using the mold clamping cylinders 13, 14, 15, and 16. Details of the clamping force in the pressure holding step will be described later. In the cooling process, the molten resin in the cavity 2a is cooled and solidified by cooling water passing through a cooling pipe (not shown) passing through the fixed mold 12 and the movable mold 22.
Then, the pressure holding process ends at time t4 shown in FIG. At time t5, the cooling process is completed, and the valve 53 of the pressurized air injection device 50 is closed to complete the air injection process. Next, at time t5, the mold 2 is opened by shifting to the mold opening process. At time t6 shown in FIG. 6, a product take-out process is executed to take out the injection-molded product 40 from the mold 2 (also see FIG. 4).

Here, as described above, the period from the start of the filling process at time t1 to the end of the pressure holding process at time t4 is accompanied by injection of the molten resin (filling process) and replenishment (pressure holding process). A corresponding internal pressure (mold internal pressure) is generated in the cavity 2a. Therefore, it is necessary to clamp the mold 2 with a suitable pressure. FIG. 7 shows an example of the mold clamping force (calculated value), the speed of the screw 33 of the injection cylinder 30 and the actual mold internal pressure (pressure in the cavity 2a) during this period.
The dotted line in the uppermost graph in FIG. 7 shows the necessary clamping force required to maintain the state where the mold 2 is completely closed. The required clamping force is calculated in advance based on the shape of the injection molded product 40, the type of the molten resin, the position of the gate 12a that injects the molten resin into the cavity 2a, and the like. In this embodiment, the required clamping force increases in proportion to the time from time t1 to time t3 (at the end of the filling process), and is calculated as f2 (N) at time t3. When the pressure holding process is started, the pressure decreases to f1 (N), and is calculated to maintain f1 (N) until time s1 (midway of the pressure holding process). Then, it is calculated so as to decrease in proportion to the time from time s1 to time t4 (at the end of the pressure holding process) and to be 0 (N) at time t4.

  In the present embodiment, in the filling process from time t1 to time t3, the actual mold clamping force (the pressure indicated by the solid line in the uppermost graph in FIG. 7) is the required mold clamping pressure (the uppermost mold in FIG. 7). The pressure is set lower than the pressure indicated by the dotted line in the graph. That is, it increases in proportion to time from time t1 to time t3 (filling step), and is set to f1 (N) at time t3. And it is set so that f1 (N) may be maintained from time t3 to time s1 (midway of the pressure holding process). Then, from time s1 to time t4 (at the end of the pressure holding process), the time decreases in proportion to the time and is set to 0 (N) at time t4. When the mold clamping cylinders 13 to 16 are controlled so that the mold clamping force is generated and the mold clamping is performed, the mold 2 is intentionally opened by about 0.1 to 0.15 mm in the filling process. With this size, even when the mold 2 is in an opened state, there is little risk of burrs occurring in the injection molded product 40 due to the molten resin entering the space between the opened molds.

  In the filling process, the speed of the screw 33 of the injection cylinder 30 is stepwise controlled as shown in FIG. The speed of the screw 33 is increased in proportion to the time after the filling process is started at time t1, and gradually decreased after reaching the peak value on the way. In the pressure holding step, the pressure of the screw 33 is controlled, so that the screw 33 is maintained at a small speed. And it is 0 when the pressure holding process is completed at time t4.

As a result, the actual in-mold pressure (pressure just below the gate 12 in the cavity 2a) increases in proportion to time from time t1 to time t3 (filling process), and reaches the peak p1 at time t3 at the end of the filling process. (MPa), enters the pressure holding process, decreases slightly, stabilizes at p2 (MPa), decreases at time s1 as the clamping force decreases and decreases to 0 (MPa) at time t4.
When the mold clamping cylinders 13 to 16 are controlled to perform mold clamping, if the necessary mold clamping force (pressure indicated by the dotted line in the uppermost graph in FIG. 7) is controlled, the pressure inside the mold during the filling process is controlled. The peak value (pressure indicated by a dotted line in the lowermost graph in FIG. 7) increases. In the injection molding method of the present invention, in the filling step, the mold 2 is intentionally maintained in a state of being opened about 0.1 to 0.15 mm. This can be said that, during the filling process, in the case of the injection-molded product 40, the space between the cavities 2a corresponding to the thickness is kept 0.1 to 0.15 mm wide. FIG. 8 shows an experimental result that the thicker the injection-molded product is (the wider the space between the cavities 2a), the wider the passage of the molten resin in the cavity 2a, and the molten resin is easily filled even at a lower filling pressure. It is shown. Therefore, according to the present embodiment, the filling pressure of the molten resin can be reduced without generating burrs in the injection molded product 40. Thereby, the internal pressure of the shaping | molding die 2 can be reduced.
Further, the mold clamping force f1 (N) is such that the value obtained by integrating the mold internal pressure p2 (MPa) in the pressure holding process in the mold clamping direction is smaller than the mold clamping force f1 (N) in the pressure holding process. Preferably it is set. As a result, when the pressure inside the mold is stable at p2 (MPa) during the pressure-holding process, the mold is completely closed, and even if the mold 2 is slightly opened during the filling process, the thickness of the finished product of the injection-molded product 40 is increased. Has no effect.

  According to the injection molding method of the present embodiment, the clamping force applied to the molding die 2 in the filling process is necessary for maintaining the molding die 2 in a completely closed state against the filling pressure. Lower than. For this reason, in the filling process, the mold 2 is slightly opened by the filling pressure of the molten resin. As described above, a high filling pressure is required to fill the cavity 2a with a narrow interval with the molten resin. In other words, if the interval between the cavities 2a is wide, the filling pressure necessary for filling the cavities 2a is lowered. If the mold 2 is slightly opened in the filling process, the space between the cavities 2a is widened. As a result, the filling pressure necessary for filling the cavity 2a can be reduced. Therefore, the mold pressure acting on the cavity surfaces 12b and 22b can be reduced, and the peak value of the mold pressure generated at the end of the filling process can be lowered. Thereby, the pressure resistance required for the mold 2 can be reduced, and the strength required for the mold 2 can be reduced. And the shaping | molding die 2 can be reduced in size and the production cost of the shaping | molding die 2 can be reduced. As a result, the production cost of the injection molded product 40 can be reduced.

  In the injection molding method of this embodiment, the clamping force applied to the molding die 2 in the filling step is set to a force that opens the molding die 2 by 0.1 to 0.15 mm by the filling pressure of the molten resin. Generally, if the mold 2 is opened more than 0.15 mm, burrs are likely to occur in the injection molded product 40. Even if the mold 2 is opened, the molten resin does not enter the gap if the gap is 0.15 mm or less. It has been confirmed that burrs are unlikely to occur in the injection molded product 40. In this case, the amount of opening of the mold becomes 0 because the process proceeds and the pressure inside the mold decreases, and it has been confirmed that even if the mold 2 is opened during filling, the thickness of the injection molded product 40 is not affected. In general, when the mold 2 is opened by 0.1 mm or more, a phenomenon that the space between the cavities 2a is widened and the filling pressure necessary for filling the cavities 2a is reduced becomes remarkable. Therefore, the required filling pressure can be reduced by widening the gaps of the cavities 2a within a range where no burrs are generated in the injection molded product 40, and the injection molding product 40 of good quality can be molded with the simple mold 2. it can.

Further, in the injection molding method of the present embodiment, since the pressure holding step is performed, it is possible to replenish the amount of molten resin contracted in the cavity 2a. Thereby, it is possible to prevent sink marks and voids from occurring in the injection molded product 40.
Further, in the injection molding method of the present embodiment, the step of injecting the pressurized fluid is performed, so that the surface (design surface) of the injection molded product 40 keeps in close contact with the first cavity surface 12b even when the molten resin contracts. . Thereby, the design surface of the injection molded product 40 can be finished in the intended shape.
Moreover, the holding pressure required in the pressure-holding step can be reduced by performing the step of injecting the pressurized fluid. By performing the pressure holding step, the pressure of the fluid to be injected toward the resin filled in the cavity 2a can be reduced. In the stage of filling the molten resin, the filling pressure can be lowered by widening the interval between the cavities 2a. These are combined together, the peak value of the pressure (in-mold pressure) applied to the cavity surfaces 12b and 22b can be reduced, and the maximum value of the clamping force applied to the mold 2 can be reduced. And the intensity | strength required for the shaping | molding die 2 can be reduced and the shaping | molding die 2 can be reduced in size. Further, the mold clamping force can be reduced, and the mold clamping mechanism including the piston shafts 43, 44, 45, 46, the mold clamping cylinders 13 to 16, and the like can be downsized. And the injection molding apparatus 1 can be reduced in size.

In the present embodiment, the case where the pressurized fluid is pressurized air has been described, but the pressurized fluid may be a gas or liquid other than air.
In the present embodiment, the case where the mold clamping force is set so that the 0.1-0.15 mm mold is intentionally opened in the filling process has been described. However, if at least the cavity 2a is secured (at least if the cavity can be filled with molten resin), the mold clamping force is lower than the necessary mold clamping force for maintaining the mold completely closed. It only has to be set. This is because some injection molded products are allowed to generate burrs.
In the present embodiment, the case where the molding die 2 is completely closed when the in-mold pressure is stable at p2 (MPa) during the pressure-holding step has been described. It is only necessary to be closed by the end of the pressure holding process.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
For example, if the filling pressure of the molten resin is high and the clamping force is large and the inner pressure and clamping force in the pressure holding process do not have to be low, both the pressure holding process and the air injection process should be performed. Is not necessarily required.
In addition, the technical elements described in the present specification or drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

The state before closing the shaping | molding die 2 is shown about the injection molding apparatus 1 used by a present Example. The mold 2 of the injection molding apparatus 1 is closed, and the injection cylinder 30 for injecting the molten resin is shown in a state where the injection cylinder 30 is in contact with the molten resin injection gate 12a of the fixed mold 12. A state in which molten resin is being injected from the injection cylinder 30 into the cavity 2a is shown. The state which opened the shaping | molding die 2 and took out the injection molded product 40 is shown. It is a figure explaining the apparatus 50 which inject | pours pressurized air into the molded article back surface side of the molten resin with which the cavity 2a was filled. The process figure of the injection molding method of a present Example is shown. It is a figure explaining the relationship between a mold clamping force and a mold internal pressure. The result of experiment that the pressure which injects molten resin may be so small that the thickness of the injection molded product 40 is large is shown. It is a figure which shows a prior art. It is a figure which shows the prior art which implements an air injection process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Injection molding apparatus 2 Injection mold 2a Cavity 3 Base 10 Fixed side apparatus 11 Fixed side platen 11a Recessed part 12 Fixed mold 12a Gate 12b 1st cavity surface 13, 14, 15, 16 Clamping cylinder 13a, 15a In-cylinder 13b, 14b, 15b, 16b Through hole 17 Mold closing cylinder 17a Piston shaft 20 Movable device 21 Movable platen 22 Movable die 22b Second cavity surfaces 23b, 24b, 25b, 26b Holes 23c, 24c, 25c, 26c Half nuts 27, 28 Flow path 27a, 28a Vent member 30 Injection cylinder 31 Nozzle head portion 32 Hollow portion 33 Screw 40 Injection molded product 43, 44, 45, 46 Piston shaft 50 Pressurized air injection device 51 Filter 52 Regulator 53 Valve 54 Fluid piping 54a Fluid piping One end of

Claims (6)

Applying a clamping force to the injection mold and closing the injection mold;
A filling step of filling the cavity in the injection mold with a molten resin in a state where a clamping force is applied to the injection mold;
A cooling step for cooling the molten resin filled in the cavity;
It has a process of opening the injection mold and taking out the injection molded product from the injection mold.
The mold clamping force applied to the injection mold in the filling step is set lower than the mold clamping force required to keep the injection mold completely closed against the filling pressure of the molten resin. An injection molding method characterized by the above. The mold clamping force applied to the injection mold in the filling step is set to a force that opens the injection mold by an interval that does not cause burrs in the injection molded product by a filling pressure of the molten resin. Injection molding method. 2. The injection molding method according to claim 1, wherein the clamping force applied to the injection mold in the filling step is set to a force that opens the injection mold by 0.1 to 0.15 mm in the filling step. Following the filling step, the pressure holding step of additionally filling the cavity with the molten resin by continuously applying pressure to the molten resin filling the cavity with the clamping force applied to the injection mold is performed. The injection molding method according to claims 1 to 3. The injection mold includes a mold for molding a design surface of an injection molded product, and a mold for molding the back surface of the injection molded product,
4. The injection molding method according to claim 1, wherein an injection step of injecting a pressurized fluid is performed between a mold for molding the back surface and the resin filled in the cavity. The injection mold includes a mold for molding a design surface of an injection molded product, and a mold for molding the back surface of the injection molded product,
Following the filling step, with the clamping force applied to the injection mold, a pressure holding step for continuously filling the cavity with the molten resin that continues to apply pressure to the cavity and a mold for molding the back surface The injection molding method according to claim 1, wherein both the injection step of injecting a pressurized fluid between the resin filled in the cavity and the resin are simultaneously performed.

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