JP3872446B2 - Injection molding method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an injection molding method for performing molding under individual conditions for each cavity when performing injection molding with a mold having a plurality of cavities.
[0002]
[Prior art]
Conventionally, various methods have been proposed for an injection molding method that uses a mold having a plurality of cavities and performs molding under individual conditions for each cavity.
[0003]
For example, injection / holding pressure is performed several times during one molding, and the runner opening / closing device provided in the molding die controls the timing of filling the resin by cavity, so that different shaped cavities are not filled simultaneously, An invention has been disclosed that aims at the effect of efficient molding by determining the order of filling by the required cooling time in a method that stabilizes the amount of resin filled in each cavity by filling with shifting time. (For example, refer to Patent Document 1).
[0004]
Also, a resin pressure sensor that detects the pressure of the resin gate cylinder and the cavity filling resin is provided in each of the resin passages to each cavity, and when the resin is filled in the first cavity, the injection pressure is controlled by feedback from the resin pressure sensor. Then, after a predetermined process is completed, an invention is also disclosed which aims to enable stable molding by repeating the same control to the second cavity and molding a plurality of cavities ( For example, see Patent Document 2).
[0005]
[Patent Document 1]
JP 7-40393 A [Patent Document 2]
JP-A-2001-205656 [0006]
[Problems to be solved by the invention]
In a conventional injection molding method in which molten resin is filled into a plurality of cavities having different shapes, the one disclosed in Patent Document 1 controls the position and speed of the forward stop of the injection screw according to the individual process of each cavity. The holding pressure is applied from the filling completion position for each cavity.
[0007]
However, since the screw position at the completion of holding pressure varies depending on the variation in resin temperature, density, and check ring closing time, the injection start position when injecting molten resin into the next cavity is shot-by-shot. However, since the holding pressure switching position is performed at the set stroke position, the actual resin volume up to the filling completion setting position may change from shot to shot. There was a possibility of causing molding defects.
[0008]
Moreover, although what was disclosed by patent document 2 is switching to pressure control and 2nd shaping | molding with the resin pressure sensor in a metal mold | die, installing a resin pressure sensor in a metal mold | die, cost is changed. Can be expensive. Moreover, there is a possibility that a molding defect may occur due to a deviation of the zero point of the resin pressure sensor due to temperature fluctuation.
[0009]
Therefore, the present invention is stable without being affected by the injection start position of the screw that fluctuates from shot to shot when filling molten resin into a plurality of cavities of different shape sizes, and is stable and stable. It is an object of the present invention to provide an injection molding method capable of performing molding.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the injection molding method of the present invention injects molten resin in a cylinder accumulated in front of a screw into a spru formed in a mold by advancing the screw and communicates with the sprue. And an injection molding method for obtaining a molded product by sequentially filling each cavity through a communication path communicating with each of a plurality of cavities of different shape sizes formed in the mold. In
The screw retracted in the sucking step after the injection step of injecting the molten resin into one of the cavities and the pressure holding step of applying a holding pressure to the molten resin in the cavity. Memory for setting the current position and the position of the screw when starting another injection process for injecting the molten resin into the other cavities not yet filled with the molten resin following the suck back process A step of calculating a difference from a set reference value stored in the means, a step of correcting the screw position when starting the other injection step by the difference, and an injection speed based on the difference in advance. And a step of correcting the switching position / holding pressure switching position .
[0011]
As described above, the injection molding method of the present invention can be applied to the other cavities following the completion of the sucking process after the injection process and the pressure holding process for one of the cavities having different shape sizes. On the other hand, when starting another injection process, the difference between the current position of the screw after the completion of the suck back process and a preset reference value is calculated, and the other injection process is performed using this difference. Correct the position of the screw at the start. That is, the injection molding method of the present invention corrects the screw position before starting the subsequent injection process every time when one shot to one cavity is completed. It is possible to correct the fluctuation of the screw position due to the variation of the screw.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
[0016]
FIG. 1 is a side sectional view of a part of an injection molding apparatus of an injection molding machine according to this embodiment and a molding die. FIG. 2 is a process diagram for explaining each process of injection molding in the present embodiment, and FIG. 3 is a flowchart of each process.
[0017]
The runner A and runner B used in the following description may be either the first runner 4a or the second runner 4b shown in FIG. 1, but here the first runner 4a is the runner A. The second runner 4b will be described as runner B. That is, in the process diagram of FIG. 2, in the process marked with A (A: injection, A: holding pressure, A: suckback), the molten resin is supplied to the first cavity 5a via the first runner 4a. The steps marked with B (B: injection, B: holding pressure, B: suckback) show the steps to be supplied to the second cavity 5b via the second runner 4b. It will be described as
[0018]
Moreover, the actual screw position shown by the solid line in FIG. 2 shows the actual position of the position of the screw 1, and a process with B (B: injection, B: pressure holding, B: suckback) ) And subsequent figures show the position of the screw 1 corrected by the difference C described later.
[0019]
The injection molding machine according to the present embodiment includes a cylinder 2 and an injection device having a screw 1 inserted into the cylinder 2 so as to be able to rotate and move forward and backward, a runner opening / closing control device 7 described later, and mechanical control for controlling the injection device. The molding die used in the injection molding machine of the present embodiment has a fixed die 9 and a movable die 10 that slides by a driving device (not shown) of the injection molding machine. .
[0020]
The machine control device 8 stores a setting reference value B, which is a preset value, for setting the position of the screw 1 at the start of injection, and a current detected by a sensor (not shown). A difference calculating unit 8b that calculates the difference C by comparing the position of the screw 1 and the set reference value B.
[0021]
The fixed mold 9 is provided with a sprue 3 through which molten resin injected from the cylinder 2 of the injection molding machine passes, and the first runner 4a and the second runner 4b of the movable mold 10 to be described later. A first runner opening / closing device 6a and a second runner opening / closing device 6b for opening and closing are incorporated. In the first runner opening / closing device 6a and the second runner opening / closing device 6b, cylinders 6a1, which are slid by hydraulic pressure or air supplied from the runner opening / closing control device 7 based on the control signal of the machine control device 8, respectively. A cylinder 6b1 is incorporated. When closing the first runner 4a, based on the control signal of the machine control device 8, the runner opening / closing control device 7 extends the cylinder 6a1 of the first runner opening / closing device 6a into the first runner 4a, When opening the first runner 4a, the cylinder 6a1 is retracted. In FIG. 1, the first runner 4a is opened when the cylinder 6a1 of the first runner opening / closing device 6a is retracted, while the cylinder 6b1 of the second runner opening / closing device 6b is in the second state. The second runner 4b is in a closed state by extending into the runner 4b, so that a state in which the molten resin can be supplied only into the first cavity 5a described later is shown.
[0022]
Further, in FIG. 1, the first runner opening / closing device 6a and the second runner opening / closing device 6b are respectively disposed on the first runner 4a and the second runner 4b, but the present invention is not limited to this. The sprue 3 is disposed in a communication path that allows the first cavity 5a and the second cavity 5b to communicate with each other, and the supply of the molten resin to the first cavity 5a and the second cavity 5b is provided at a controllable position. For example, it may be arranged in the first gate 11a and the second gate 11b which are entrance portions of the first cavity 5a and the second cavity 5b.
[0023]
The movable mold 10 is connected to the first runner 4a and the second runner 4b through which the resin passes, the runners 4a and 4b, and a first cavity 5a and a first cavity that form a final product shape. A second cavity 5b having a larger shape size than that of 5a, that is, having a larger capacity is formed.
[0024]
Next, the injection molding process of the present embodiment will be described with reference to FIG. 2 which is a process diagram in which the screw position and each process of one example of the injection molding method of the present embodiment correspond to each other. Reference numerals S1 to S13 (S5 to S7 are not shown in FIG. 2) indicating the respective steps correspond to the flowchart of FIG. 3 to be described later.
[0025]
First, a mold closing process for closing the molding die is performed, the runner A is opened, and the runner B is closed (S1).
[0026]
Thereafter, resin is injected into the molding die in the injection step A which is the first injection step (S2).
[0027]
At the completion timing of filling, the pressure is maintained in the pressure-holding step A for compensating for the shrinkage of the resin, and the molding of the first cavity is completed (S3).
[0028]
Thereafter, in order to release the pressure, suck back is performed in the suck back step A (S4), the runner A is closed, and the runner B is opened (S5).
[0029]
Next, the second cavity is molded. At this time, the injection start position is calculated by comparing the preset reference value B set in advance with the current screw position to calculate the screw position difference C (S6). Then, with this difference C, the injection speed switching position / holding pressure switching position (not shown) is corrected in advance (S7).
[0030]
Thereafter, in the injection step B which is the second injection step, the resin is injected into the molding die (S8), and the pressure is maintained in the pressure-holding step B to compensate for the shrinkage of the resin at the timing of filling completion ( S9). The screw switching position in switching from injection to holding pressure is performed at the screw position corrected with the difference C.
[0031]
After the suck back step (S10), when the filling of the second cavity is completed, the plasticizing operation of the material is performed (S11), the mold is opened after the cooling time necessary for the product has elapsed (S12), and the product Is taken out (S13).
[0032]
Next, each process described above will be described with reference to the injection molding machine shown in FIG. 1 and FIG. 3 which is a flowchart showing each molding process.
[0033]
At the start of molding, in response to an instruction from the machine control device 8 to the runner opening / closing control device 7, the cylinder 6b1 of the runner opening / closing device 6b operates in the runner closing direction, and a second flow path of molten resin to the second cavity 5b. The runner 4b is cut off. In this state, the fixed mold 9 and the movable mold 10 are closed in the mold closing process. Thereafter, the cylinder 6a1 of the runner opening / closing device 6a operates in the runner opening direction, and the first runner 4a, which is a flow path of molten resin to the first cavity 5a, is opened (S1).
[0034]
Next, in the injection process A, the screw 1 is advanced to inject the molten resin stored in front of the cylinder 2 into the sprue 3. The molten resin passes through the sprue 3 and flows into the first runner 4a. Here, since only the cylinder 6a1 of the runner opening / closing device 6a is open, the molten resin flows into the first cavity 5a. On the other hand, since the second runner 4b is closed by the cylinder 6b1 of the runner opening / closing device 6b, the molten resin does not flow into the second cavity 5b (S2).
[0035]
When the filling of the molten resin into the first cavity 5a is completed and the pressure holding step A is completed (S3), the operation of the suck back A is performed (S4). Thereafter, in response to an instruction from the machine control device 8 to the runner opening / closing control device 7, the cylinder 6a of the first runner opening / closing device 6a is actuated in the runner closing direction, which is a flow path of the molten resin to the first cavity 5a. The first runner 4a is cut off, the cylinder 6b1 of the second runner opening / closing device 6b operates in the runner opening direction, and the second liner 4b, which is the flow path of the molten resin to the second cavity 5b, is opened. (S5).
[0036]
Thereafter, the difference calculation unit 8b of the machine control device 8 compares the current screw position detected by the sensor with the set reference value B to calculate the difference C (S6). At C, the injection speed switching position / holding pressure switching position is corrected (S7).
[0037]
In this state, the resin melted by the molding machine in the injection process B passes through the sprue 3 and flows into the second runner 4b (S8). Here, since only 6b is open in the runner opening / closing devices 6a and 6b, the molten resin flows into the second cavity 5b. Since the runner opening / closing device 6a is in the closed state, the molten resin does not flow into the first cavity 5a.
[0038]
When the filling of the resin into the second cavity 5b is completed and the pressure holding process B (S9) is completed, the operation of the suck back B (S10) is performed.
[0039]
Thereafter, in response to an instruction from the machine control device 8 to the runner opening / closing control device 7, the second runner opening / closing cylinder 6b is operated in the runner closing direction so that the flow path of the molten resin is blocked, and the screw 1 is rotated. Then, the molten resin is metered.
[0040]
Finally, the material is plasticized (S11), and after the cooling time required for the product has elapsed, the fixed mold 9 and the movable mold 10 are opened (S12), and the product is taken out (S13).
[0041]
In this embodiment, the number of repetitions of the injection / holding process is two, but it can be repeated a plurality of times in the same manner.
[0042]
As described above, according to the injection molding method of the present embodiment, the filling into the first cavity 5a is performed by the method of switching the injection speed / holding pressure at the normal set screw position, and the second For the cavity 5b, a position where the resin filling of the first cavity 5a is completed is compared with a set reference value B which is a preset injection start position for molding the second cavity 5b. And the injection speed switching position / holding pressure switching position is corrected for each shot. For this reason, since it is possible to correct fluctuations in the screw position due to fluctuations in resin temperature, density fluctuations, check ring closing time variation (not shown), etc., the remaining time for each shot when the first cavity 5a is formed is corrected. It is possible to eliminate the weight variation and molding failure in the second cavity 5b that may occur due to the amount fluctuation, and it is possible to perform stable molding without providing a resin pressure sensor in the mold.
[0043]
【The invention's effect】
As described above, according to the present invention, after the completion of the sucking process after the injection process and the pressure holding process for one of the plurality of cavities, another injection is performed for the other cavities. Every time the process is started, the difference between the current position of the screw and the set reference value is calculated, and this difference is used to correct the position of the screw when starting another injection process.・ Screw position fluctuations due to changes in density and check ring closing time can be corrected, and stable molding can be performed without providing a resin pressure sensor in the mold.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of a mold / molding machine for realizing an injection molding method of the present invention.
FIG. 2 is a process diagram in which a screw position and each process in an embodiment of an injection molding method according to the present invention are associated with each other.
FIG. 3 is a flowchart of an embodiment of an injection molding method according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Screw 2 Cylinder 3 Sprue 4a 1st runner 4b 2nd runner 5a 1st cavity 5b 2nd cavity 6a 1st runner opening / closing device 6a1, 6b1 Cylinder 6b 2nd runner opening / closing device 7 Runner opening / closing control device 8 Machine control device 8a Storage unit 8b Difference calculation unit 9 Fixed mold 10 Movable mold 11a First gate 11b Second gate

Claims (2)

The molten resin in the cylinder collected in front of the screw is injected into the sprue formed in the mold by moving the screw forward, communicated with the sprue, and the shape size formed in the mold In the injection molding method for obtaining a molded product by sequentially filling each of the cavities through a communication path communicating with each of a plurality of different cavities and performing molding,
The screw retracted in the sucking step after the injection step of injecting the molten resin into one of the cavities and the pressure holding step of applying a holding pressure to the molten resin in the cavity. Memory for setting the current position and the position of the screw when starting another injection process for injecting the molten resin into the other cavities not yet filled with the molten resin following the suck back process Calculating a difference from a set reference value stored and held in the means;
A step of correcting the position of the screw when starting the other injection step by the difference;
Correcting the injection speed switching position / holding pressure switching position in advance using the difference; and
An injection molding method comprising: Before the injection step for the one cavity, the step of closing the communication path communicating with the other cavity and the suck back step for the one cavity are finished, and then the communication communicating with the one cavity is completed. The injection molding method according to claim 1 , further comprising a step of closing the passage.

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