JP2003103594A - Injection molding method and injection molding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a dwell pressure from becoming insufficient while the peak value of an injection pressure is reduced. SOLUTION: An automotive front bumper 1 as an injection molded product has a special shape part 2 such as a lattice shape which becomes a fine shape part on a part of the bumper 1. A material for injection molding is injected into a cavity 34 of a mold 31 from a screw-type injection device 21. A plurality of gates 11 to 14, of the molding pattern 31, through which the material passes, are provided, and each of the gates 11 to 14 is equipped with opening/closing valves 41 to 44. Further, the gates 11 and 12 which are open in the cavity 34 near a position corresponding to the special shape part 2, are closed when a screw 23 is positioned as specified halfway through an injection process and remain closed until a dwelling process is halfway after completion of the injection. When a first time T1 is past since the start of the dwelling process, the gates 11 and 12 are once opened to increase the dwell pressure. Finally, when a second time T2 is past since the start of the dwelling process, the gates 11 and 12 are again closed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an injection molding method and an injection molding apparatus.

[0002]

2. Description of the Related Art In injection molding, a material is injected from a screw type injection means into a cavity defined in a mold through a gate provided in the mold. After the injection of the material into the cavity, the mold is closed and the pressure is maintained until the material cools.After this pressure holding process, the mold is opened and the shape of the cavity is adjusted. The injection molded product is taken out. Further, there is also one in which a plurality of gates are provided for one cavity, and an opening / closing means is provided for each of the plurality of gates.

The injection pressure has a great influence on the quality of the product, and in particular, when the peak value of the injection pressure becomes too large, it becomes a major cause of product defects. On the other hand, injection pressure tends to increase because a large-sized and thin-walled product such as a bumper of an automobile is being injection-molded.

In order to increase the injection pressure and reduce the peak value of the injection pressure, the opening / closing means of a specific part of the plurality of gates is switched from the open state to the closed state during the injection. , The peak value of the injection pressure is reduced (for example, Japanese Patent Laid-Open No. 6-2
No. 38719).

[0005]

By the way, in a large-sized product which is required to be injection-molded, a part thereof has a lattice-like (mesh-like or mesh-like) structure as compared with other parts. In some cases, it may be a specific shape part that is a fine shape part of. For example, in a front bumper for an automobile, it has been required to perform injection molding with a specific shape portion of a lattice-like portion of the intake of traveling wind as a specific shape portion.

As described above, in the case where the injection-molded article partially has the specific shape portion, the injection pressure to the portion corresponding to this specific shape portion may be increased similarly to the injection pressure to the other portions. However, burrs are generated on the specific shape portion or the specific shape portion is crushed. Therefore, it is conceivable that the gate (opening / closing means provided in the gate) near the portion corresponding to the specific shape portion is closed during the injection in order to reduce the peak value of the injection pressure.

However, if the opening / closing means is closed so as to reduce the peak value for the specific shape,
It was found that in the pressure-holding process after the completion of injection, the pressure-holding pressure including the specific shape portion becomes insufficient, which causes a product defect.

The present invention has been made in consideration of the above circumstances, and an object thereof is to prevent the situation where the holding pressure is insufficient while reducing the peak value of the injection pressure. Another object of the present invention is to provide an injection molding method and an injection molding device.

[0009]

In order to achieve the above object, the method of the present invention adopts the following solution method. That is, as described in claim 1 in the claims, the material is injected by the injection means into the cavity of the mold through the plurality of gates having the opening / closing means, and further, during the injection of the material by the injection means,
In an injection molding method in which a specific opening / closing means provided in a specific part of a plurality of gates is switched from an open state to a closed state, the specific opening / closing means is closed during the injection of the material. After the injection of the material, the closed state is maintained until the middle of the pressure-holding process after the completion of the injection of the material, and the valve is once opened and then closed again during the pressure-holding process. The peak value of the injection pressure can be reduced by switching the specific opening / closing means from the open state to the closed state during the injection. Then, in the pressure-holding process, the pressure of the pressure-holding is sufficiently secured by temporarily opening the specific opening / closing means that was conventionally kept closed.

Based on the above solution method, the following solution methods can be adopted together. That is, the injection means is a screw type, and the timing at which the specific opening / closing means is closed during the injection is when the screw of the injection means is displaced to a predetermined first position, and in the pressure holding process. The timing for opening the specific opening / closing means is when a predetermined first time has elapsed from the start of pressure holding, and the timing for closing the specific opening / closing means opened in the pressure holding process is The predetermined second time, which is longer than the first time, has elapsed from the start of the holding pressure, and the second time may be set. The displacement position of the screw serves as a parameter indicating the amount of material filled in the cavity. Further, in the pressure-holding process, by setting the timing of the opening operation and the closing operation in a specific opening / closing state using the elapsed time from the pressure-holding start as a parameter, it is possible to easily manage a suitable holding pressure in the pressure-holding process. be able to.

The timing at which the specific opening / closing means is closed during the injection is that the screw is displaced in the injection direction above the first position, and the injection pressure by the injection means exceeds a predetermined value. If both conditions are met, it can be set as such. In this case, the measurement of the filling amount of the material in the cavity can be managed more accurately by using the injection pressure as a parameter together with the screw position.

The timing at which the specific opening / closing means is closed during the injection is that the screw is displaced in the injection direction above the first position and that the pressure inside the cavity is above a predetermined value. When both conditions of and are satisfied, it can be set as. In this case, the measurement of the filling amount of the material in the cavity can be managed more accurately by using the pressure in the cavity together with the screw position as a parameter.

A product to be injection-molded has a specific shape part which is finer than the other part in a part thereof, and the specific part of the gate is included in the mold cavity. The gate may be opened at a position corresponding to the vicinity of the specific shape portion. In this case, the specific shape portion and the other portions can be accurately injection-molded into desired shapes.

An injection molding apparatus corresponding to the above-mentioned injection molding method, claims 6 to 10 in the claims.
It is provided as an aspect as described in 1.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 1 is an injection-molded article molded by an injection-molding method and an injection-molding apparatus according to the present invention, which is a front bumper of an automobile in the embodiment. The front bumper 1 has a specific shape portion 2 which is a finer shape portion than other portions in the lower center of the vehicle width direction. In the embodiment, the specific shape portion 2 has a lattice-like structure in which a large number of small holes are partitioned by fine line portions. The other parts than the specific shape part 2 do not have fine small holes, and are configured to form a large area part as a whole. It should be noted that, on the left and right of the specific shape portion 2, there are formed relatively large openings 3 for taking in traveling wind for cooling the front wheel brake.

The positional relationship of the plurality of gates in the injection mold with respect to the front bumper 1 as an injection molded product is shown in FIG. In the embodiment shown in FIG. 2, the gates are the first gate 11, the second gate 12, and the third gate 1.
A total of four third gates 14 are provided. The first gate 11 and the second gate 12 are vertically spaced at a substantially central portion of the front bumper 1 in the vehicle width direction so as to be located near the specific shape portion 2, and the specific shape portion is provided therebetween. 2 is set to be located. The third gate 13 is positioned near the left opening 3, and the fourth gate 14 is positioned near the right opening 3.

Each of the gates 11 to 14 has a common line 15 to a branch line 16 formed on the molding die.
The injection molding material is supplied via 17, 18 or 19. Each of the first gate 11 to the fourth gate 14 is a hot runner.

FIG. 3 shows an outline of the entire injection molding apparatus. Reference numeral 21 is an injection device (injection means), and 31 is a molding die. The injection device 21 is a screw type in the embodiment. That is, the injection device 21 includes the cylinder 2
2. A screw 23 rotatably and slidably installed in the cylinder 22, a hydraulic cylinder 24 for generating injection pressure, and a rotary drive mechanism 25 for the screw 23. And
The weighed material in the cylinder 22 which receives the pressing force of the screw 23 is injected from the injection port 22a to the above-mentioned common line 15 of the molding die 31.

The molding die 31 has a first molding die 32 and a second molding die 33 which are opened and closed with each other and constitutes a cavity 34 when closed. The shape of the cavity 34 corresponds to the shape of the front bumper 1 described above.
The above-described four gates 11 to 14 are mounted on the first molding die 32 and opened in the cavities 34, respectively.

4 and 5 showing the details of the molding die 31, the above-mentioned four gates 11 to 14 are equipped with opening / closing valves 41 to 44 as opening and closing means (2 for the opening 3). The two on-off valves 43, 44 are shown only schematically in relation to the gates 13, 14 in FIG. 2). Each of the on-off valves 41 to 44 has the same structure and has a valve seat 41A provided in the vicinity of the cavity 34 and a rod-shaped valve body 41B that is seated on and away from the valve seat 41A. Each of the gates 41 to 44 is in a closed state when the valve body 41B is seated on the valve seat 41A, and is in an open state when the valve body 41B is separated from the valve seat 41A. Each valve element 41B is driven and displaced by a hydraulic cylinder 45 provided individually for each valve element 41B. In FIG. 5, reference numeral 46
Is a coil for heating the gate.

Referring again to FIG. 3, U is a control unit constructed by using a microcomputer, and CP
It has a U, a ROM, a RAM, a clock as timer means, and the like. The control unit U controls opening / closing of the opening / closing valves 41 to 44. Signals from the respective sensors (detection means) S1, S2, S3 are input to the control unit U. Further, from the control unit U to the hydraulic control means U2 for opening / closing control of the opening / closing valves 41 to 44, the opening / closing valves 41 to 41 are connected.
An opening / closing command signal indicating opening or closing of 44 is output.

The sensor S1 detects the oil pressure of the hydraulic cylinder 34, that is, the injection pressure. The sensor S2 detects the displacement position of the screw 23. The sensor S3 is provided on the second molding die 33 and detects the pressure in the cavity 34.

Next, the open / close control of the open / close valve by the control unit U will be described with reference to the time chart of FIG. In FIG. 6, the first gate 11 and the second gate 12
The opening / closing mode of (open / close valves 41, 42 for) is unique to the present invention, and is different from the opening / closing mode of the third gate 13 and the fourth gate 14 (open / close valves 43, 44 for). There is. First, at time t1 before injection, the first gate 11
The opening / closing valve 41 for the second gate 12 and the opening / closing valve 42 for the second gate 12 are opened, respectively, while the opening / closing valve 43 for the third gate 13 and the fourth opening / closing valve 42 are opened.
The on-off valve 44 for the gate 14 is closed.

At time t2, the injection of the material is started, and the screw 23 is displaced in the injection direction (right side of FIG. 3).
During this injection, both that the screw 23 detected by the sensor S2 is displaced to a predetermined first position or higher and that the injection pressure detected by the sensor S1 is a predetermined pressure or higher are satisfied. When the first gate 1
1 (open / close valve 41) and the second gate 12 (open / close valve 42) are closed, and this time is t4. On the other hand, the third gate 13 (open / close valve 43) and the fourth gate 14 (open / close valve 4) are switched from the closed state to the open state slightly before the time t4. The peak value of the injection pressure is reduced by closing the first gate 11 and the second gate 12 at time t4.

When the displacement position of the screw 23 in the injection direction detected by the sensor S2 reaches the second predetermined position, which is further advanced in the injection direction than the first predetermined position, the injection is completed. Becomes t5. Also, this t5
The time point is the start time point of the holding pressure after the injection is completed. This t5
Until the time point, there is no change in the open / closed state of each on-off valve, the first gate 11 and the second gate 12 remain closed, and
The gate 13 and the fourth gate 14 remain open.

The first gate 11 and the second gate 12 are opened at time t6 when a predetermined first time T1 has elapsed from time t5 when the pressure holding starts. A predetermined second time set to a time period longer than the first time period T1 from the start of holding pressure.
At time t7 when the time T2 has elapsed, the first gate 1
The first and second gates 12 are closed again. At this time, the third gate 13 and the fourth gate 14 are closed at time t8, which is slightly delayed from the second predetermined time T2.

At time t9, which is a short time after the gates 11 to 14 are closed, the screw 23 starts to be displaced in the direction opposite to the injection direction. Screw 23
At the time point t10 when the material returns to the predetermined position and returns, is the time point when the measurement of the material is started. From this time point t10, the screw 23 is returned and displaced at a considerably large speed, and the material for the next injection molding is measured (in the cylinder 22). Supply of materials). The time when the measurement of the material is completed is t11.
It corresponds to the time point and the same thing is repeated thereafter.

FIG. 7 shows the first control of the control shown in FIG.
Gate 11 (open / close valve 41), second gate 12 (open / close valve 4
The flowchart for performing the opening / closing control of 2) is shown. Hereinafter, FIG. 7 will be described. In the following description, Q indicates a step.

First, in Q1, both gates 11 and 12 are
And are opened (at time t1 in FIG. 6). At Q2, it is judged if the screw 23 is displaced in the ejection direction beyond the predetermined first position α. YES in this Q2 determination
In this case, in Q3, it is determined whether or not the injection pressure detected by the sensor S2 is equal to or higher than the predetermined pressure β. Q3
When the determination is YES, it is at time t4 in FIG. 6, and at this time, in Q4, the gates 11 and 12 are opened. If NO in the determination of Q2 or Q3,
Return to 2.

After Q4, in Q5, the screw 23
Is determined to have reached the second predetermined position α2 at which injection is completed. If YES in the determination in Q5,
It is a time point t5 in FIG. 6 and a time point when the pressure holding is started, and at this time, the first time T1 and the second time T2 are set in Q6. If the result of the determination in Q5 is NO, this Q5
The determination of is repeated.

After Q6, in Q7, the first predetermined time T1
When it is confirmed that has passed, both gates 11 and 12 are opened in Q8 (time t6 in FIG. 6). After Q8, when it is confirmed in Q9 that the second time T2 has elapsed, the gates 11 and 12 are closed in Q10 (time t7 in FIG. 6).

Although the embodiment has been described above, the present invention is not limited to this, and includes the following cases, for example. The injection device 21 is not limited to the screw type. During the injection, the first gate 11 and the second gate 1
The timing of closing 2 (at time t4 in FIG. 6) is the mold 3
It is at the time when it is confirmed that the filling amount of the material into 1 has reached the predetermined amount. Therefore, in order to know the filling amount, the following can be performed. That is, when both the conditions that the screw 23 is displaced in the injection direction above the first position and that the pressure inside the cavity 34 detected by the sensor S3 is above a predetermined pressure are satisfied. Alternatively, the first gate 11 and the second gate 12 may be closed. Further, the first gate 11 and the second gate 12 may be closed only when the screw 23 is in the first position.

The specific shape portion 2 which is a fine shape portion is not limited to the lattice shape, and an appropriate shape (structure) is applicable as long as it is a portion having a finer shape than other portions. Injection-molded articles are not limited to automobile bumpers.

Each step shown in the flow chart or various members such as a sensor and a switch can be expressed by adding a name of means to the higher level expression of the function. Further, the object of the present invention is not limited to what is specified, and also implicitly includes providing what is expressed as substantially preferable or advantageous.

[0035]

According to the present invention, it is possible to obtain a good injection-molded article by reducing the peak value of the injection pressure and further optimizing the holding pressure in the holding pressure process.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of an injection molded product.

FIG. 2 is a front view showing an example of a positional relationship between an injection molded product and a plurality of gates.

FIG. 3 is a partial side sectional view showing the entire injection device.

FIG. 4 is a side sectional view showing details of the molding die shown in FIG.

5 is an enlarged cross-sectional view of a main part of FIG.

FIG. 6 is a time chart showing a control example of the present invention.

FIG. 7 is a flowchart showing a control example of the present invention.

[Explanation of symbols]

1: Front bumper (injection molded product) 2: Specific shape part 11: First gate (specific gate) 12: Second gate (specific gate) 13: 3rd gate 14: 4th gate 21: injection device (injection means) 23: Screw 31: Mold 32: First mold 33: Second mold 34: Cavity 41: Open / close valve (specific opening / closing means) 42: Open / close valve (specific opening / closing means) 43: Open / close valve 44: Open / close valve U: Control unit (opening / closing control means) U2: Hydraulic control device S1: Sensor (injection pressure detection) S2: Sensor (screw displacement position detection) S3: Sensor (cavity pressure detection)

Continued front page    (72) Inventor Masaru Muromoto             3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda             Within the corporation F-term (reference) 4F202 AH24 AP02 AP06 AP10 CA11                       CB01 CK06 CK07                 4F206 AH24 AP024 AP062 AP10                       JA07 JD03 JL02 JN15 JN25                       JP11 JQ81

Claims (10)

[Claims] 1. A material is injected by an injection means into a cavity of a mold through a plurality of gates having opening and closing means,
Moreover, in the injection molding method in which a specific opening / closing means provided in a specific part of the plurality of gates is switched from the open state to the closed state during the injection of the material by the injection means, The opening / closing means is maintained in the closed state after being closed during the injection of the material until the middle of the pressure holding process after the completion of the injection of the material, and is once opened in the middle of the pressure holding process, and then again. An injection molding method, characterized in that the injection molding method is in a closed state. 2. The injection means according to claim 1, wherein the injection means is a screw type, and the timing at which the specific opening / closing means is closed during the injection is when the screw of the injection means is displaced to a predetermined first position. In the pressure-holding process, the timing for opening the specific opening / closing means is when a predetermined first time has elapsed from the start of the pressure-holding process, and the specific opening / closing in the pressure-holding process is performed. The injection molding method is characterized in that the timing at which the means is closed is set to a timing when a predetermined second time, which is a time longer than the first time, has elapsed from the start of the pressure holding. 3. The injection timing according to claim 2, wherein the timing at which the specific opening / closing means is closed during the injection is that the screw is displaced in the injection direction to the first position or more, and the injection pressure by the injection means. The injection molding method is characterized in that both conditions are satisfied such that the value of the value is equal to or more than a predetermined value. 4. The cavity according to claim 2, wherein the timing at which the specific opening / closing means is closed during the injection is that the screw is displaced in the injection direction above the first position, and The injection molding method is characterized in that it is determined that both conditions, that is, the internal pressure exceeds a predetermined value, are satisfied. 5. The product to be injection-molded according to any one of claims 1 to 4, wherein a part of the product to be injection-molded has a specific shape part which is finer than other parts. The injection molding method is characterized in that the specific part of the gate is a gate opened at a position corresponding to the vicinity of the specific shape part in the cavity of the molding die. 6. An injection unit for injecting a material, a mold having a plurality of gates to which the injection unit is connected and defining a cavity in which the plurality of gates are connected, and a plurality of gates provided on the plurality of gates. An opening / closing means, and an opening / closing control means for controlling the opening / closing of the opening / closing means,
The opening / closing control means switches a specific opening / closing means among the plurality of opening / closing means from an open state to a closed state during the material injection, and maintains the closed state until the halfway of the pressure holding process after the completion of the material injection. Moreover, the injection molding apparatus is characterized in that it is controlled to be in the open state and then in the closed state again in the middle of the pressure holding process. 7. The injection mechanism according to claim 6, wherein the injection means is a screw type, a position detection means for detecting a displacement position of the screw of the injection means, a first predetermined time which is an elapsed time from the start of the pressure holding, and Timer means for counting a second predetermined time period that is longer than the first predetermined time period, and the opening / closing control means has a predetermined displacement position of the screw detected by the position detection means means. The specific opening / closing means is switched from the open state to the closed state when the first predetermined time is counted, and the opening / closing means is opened when the first predetermined time is counted. An injection molding apparatus, wherein the opening / closing means is closed when the second predetermined time is counted by the timer means. 8. The pressure detecting means according to claim 7, further comprising a pressure detecting means for detecting an injection pressure by the injection means, wherein the opening / closing control means detects a displacement position of the screw detected by the position detecting means means. Displaced in the injection direction more than 1 position,
And when both the conditions that the predetermined pressure is detected by the pressure detection means are satisfied, the specific opening / closing means is switched from the open state to the closed state during the injection. Molding equipment. 9. The pressure detection means according to claim 7, further comprising a pressure detection means for detecting a pressure in the cavity, wherein the opening / closing control means detects the displacement position of the screw detected by the position detection means means as the first position. Displaced more than the position in the injection direction,
And when both the conditions that the predetermined pressure is detected by the pressure detecting means are satisfied, the specific opening / closing means is switched from the open state to the closed state during the injection. Molding equipment. 10. The product to be injection-molded according to claim 6, wherein a part of the product to be injection-molded has a specific shape part which is finer than other parts. The injection molding apparatus, wherein the specific part of the gate is a gate opened at a position corresponding to the vicinity of the specific shape part in the cavity of the molding die.