JP4619561B2 - Mold opening and closing device of injection foam molding machine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a mold opening / closing device of an injection foam molding machine, and more particularly to a mold opening / closing device of an injection foam molding machine capable of accurately controlling a mold opening amount of a mold necessary for foam molding.
[0002]
[Prior art]
In recent years, foam molding has attracted attention in order to reduce the weight of a plastic molded product and to add a soft feeling to the contact feeling of the molded product. In this type of foam molding, a resin containing a foaming agent is injected into a cavity in a mold by an injection molding machine. Foam molded products are widely used, for example, as interior materials for automobiles.
[0003]
In foam molding, a resin generates a foaming gas immediately after injection, and the resin is expanded to form innumerable foamed cells. In order to mold a high-quality foam molded article, it is necessary to increase the expansion ratio so that the formation of foam cells does not become uneven.
[0004]
In view of this, the present applicant has proposed a molding method of an injection foam molded product in JP-A-8-267526, in which the foamed cells are small and uniform and the foaming ratio can be improved. In this injection foamed molding method, the resin containing the foaming agent is injected into the cavity in the mold closed state of the injection molding machine, and after the injection is completed, the resin wall is expanded by the foaming gas to maintain the contact between the mold wall surface and the resin. However, the movable mold is stopped at a preset reference wall thickness position, and after the cooling is completed, the movable mold is moved backward to take out the product. According to this molding method, after completion of the injection of the resin containing the foaming agent, the movable mold is moved while maintaining the contact between the mold wall surface and the resin by the expansion of the foam gas, so that the size of the foam cell is small and uniform. In addition, the expansion ratio is improved, and a molded product having a large elastic force can be formed even with a thin wall thickness.
[0005]
In order to implement such an injection foam molding method, it is necessary to accurately move the movable mold in accordance with the expansion of the resin by the foaming gas after the completion of injection. In a conventional injection foam molding machine, a hydraulic servo mechanism is provided in a hydraulic circuit that supplies pressure oil to a clamping cylinder that opens and closes a mold, together with a detector that detects the position of the movable mold. Is controlling.
[0006]
[Problems to be solved by the invention]
In the case of injection foam molding, it is necessary to move the mold by a very small distance in the mold opening direction in accordance with the expansion of the resin due to the generation of the foaming gas after injecting the resin containing the foaming agent by performing mold clamping. In order to keep the quality of the foam molded product constant, it is important to accurately stop the movable mold at a preset position such as the reference thickness position.
[0007]
However, in the conventional injection foam molding machine, the position and speed of the movable mold are controlled by controlling the hydraulic oil supplied to and discharged from the mold clamping cylinder. It was difficult to stabilize. Moreover, after the positioning block is sandwiched between the mold or the die plate and the resin is injected, the movable mold is moved, and the movable mold is stopped at a predetermined position by the positioning block, thereby stabilizing the movable mold opening amount. However, there is a drawback that a mechanical mechanism for positioning becomes large.
[0008]
Accordingly, an object of the present invention is to eliminate the problems of the prior art and to accurately and stably control the movement and stop of the movable mold according to the expansion of the resin by the foaming gas for foam molding. An object of the present invention is to provide a mold opening and closing device for an injection foam molding machine.
[0009]
[Means for Solving the Problems]
To achieve the above object, the present invention provides a hydraulic mold opening / closing used in an injection foam molding machine for injecting a resin containing a foaming agent into a fixed mold and a movable mold to mold a foam molded product. The apparatus includes: a mold clamping cylinder that applies a clamping force to the mold that is closed; a boost cylinder that is connected to the movable mold and moves the movable mold; and a hydraulic source, the mold clamping cylinder and the boost cylinder A first hydraulic circuit that supplies and discharges hydraulic oil to and from the mold clamping cylinder and the boost cylinder so that the cylinder operates in conjunction with each other so as to perform a series of operations for mold opening / closing and mold clamping, and a constant displacement hydraulic pump And a servo motor for driving the hydraulic cylinder, and supplying hydraulic oil to the boost cylinder for moving the movable mold to a foam molding reference position set in a mold opening direction by a predetermined distance from the mold closing position. 2 A hydraulic circuit, position detecting means for detecting the position of the movable type, and a feedback of a movable position detection signal from the position detecting means, and the movable type is moved to the reference position while comparing the detected position with the reference position. The position feedback control means for controlling the rotation of the servo motor so as to reach the reference position and the supply of pressure oil to the boost cylinder is stopped when the movable type reaches the target position. The first hydraulic circuit switching means for switching the second hydraulic circuit as described above, and the hydraulic pressure in the mold closing direction acts on the movable mold from the mold clamping cylinder against the foaming force, and the position of the movable mold is the reference And a second hydraulic circuit switching means for switching the flow path of the first hydraulic circuit so as to be held at the position.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a mold opening and closing device of an injection foam molding machine according to the present invention will be described with reference to the accompanying drawings.
FIG. 1 shows a hydraulic circuit diagram of a mold opening / closing device of an injection foam molding machine according to the present embodiment. In FIG. 1, 1 is a fixed mold and 2 is a moving mold. The fixed mold 1 is attached to the fixed die plate 3, and the movable mold 2 is attached to the movable die plate 4. An injection device is arranged on the fixed die plate 3 side. In FIG. 1, a heating barrel 5 of the injection device is shown. A screw (not shown) is mounted inside the heating barrel 5. The resin mixed with the foaming agent is melted by the rotation of the screw, and the melted resin is injected from the nozzle 6 by the advance of the screw.
[0011]
One end of a tie bar 7 is coupled to the fixed die plate 3, and the tie bar 7 extends through the movable die plate 4 to the clamping cylinder 8, and the other end of the tie bar 7 is connected to the clamping cylinder 8. ing. A ram 10 is inserted into the cylinder chamber 9 inside the mold clamping cylinder 8, and the tip of the ram 10 extending from the mold clamping cylinder 8 is coupled to the movable die plate 4.
[0012]
In this embodiment, the mold clamping cylinder 8 is for applying a mold clamping force after the stationary mold 1 and the movable mold 2 are closed. On the other hand, the pair of boost cylinders 12, 12 disposed on the left and right sides of the fixed die plate 3 moves the movable mold 2 in the direction approaching the fixed mold 1 to close the mold, Alternatively, the movable die 2 is moved in the separating direction to open the die, and the tip portions of the piston rods 13 and 13 extending outward from the boost cylinders 12 and 12 are connected to the movable die plate 4. Yes.
[0013]
Next, a first hydraulic circuit for operating the mold clamping cylinder 8 and the boost cylinder 12 at the time of mold opening / closing and mold clamping will be described.
[0014]
In FIG. 1, reference numerals 14a and 14b are multiple hydraulic pumps, and 15 is a motor for driving the hydraulic pumps 14a and 14b. Reference numeral 16 denotes a tank containing hydraulic oil. The hydraulic oil discharged from the hydraulic pumps 14 a and 14 b is supplied to the boost cylinders 12 and 12 and the mold clamping cylinder 8 after passing through the flow rate adjusting valve 17 and the mold opening / closing switching valve 18. Here, a 4 port 3 position electromagnetic switching valve is used for the mold opening / closing switching valve 18, and a pipe line extending to the cylinder chamber 12 a on the mold opening side of the boost cylinder 12 is connected to the B port. ing. One of the pipes connected to the A port is bifurcated and extends to the cylinder chamber 12 b on the mold closing side of the boost cylinder 12.
[0015]
On the other hand, the other branched pipe is connected to the P port of the clamping cylinder switching valve 20. The pipe line connected to the A port of the mold clamping cylinder switching valve 20 extends to the entrance port of the cylinder chamber 9 of the mold clamping cylinder 8. The mold clamping cylinder 8 is provided with a prefill valve 22 and an opening / closing cylinder 23 that opens and closes the prefill valve 22. When the mold is opened, the hydraulic oil in the cylinder chamber 9 is discharged to the drain side so that the mold opening operation can be performed quickly. Can be done. Reference numeral 24 denotes a prefill valve switching valve. 26 is a pressure regulating valve for setting the pressure of the hydraulic oil.
[0016]
The A port of the prefill valve switching valve 24 is connected to the lower cylinder chamber of the open / close cylinder 23 that closes the prefill valve 22, and the B port is connected to the upper cylinder chamber that is opened. While the movable mold 2 is opened and closed, the solenoid 24b of the prefill valve switching valve 24 is excited and switched to a position where the P port and the B port communicate with each other, and the prefill valve 22 is opened. Eight cylinder chambers 9 are in communication with the drain side.
[0017]
In this state, when the solenoid 18b of the mold opening / closing switching valve 18 is energized, the P port and the A port communicate with each other, and hydraulic oil is supplied to the cylinder chamber 12b on the mold closing side of the boost cylinder 12 so that the moving mold 2 is moved to the right. When the solenoid 18a is energized, the P port and the B port communicate with each other, and hydraulic oil is supplied to the cylinder chamber 12a on the mold opening side, so that the movable mold 2 opens to the left. Yes.
[0018]
At the time of mold clamping, the solenoid 24a of the prefill valve switching valve 24 is excited while the movable mold 2 is closed to switch to a position where the P port and the A port communicate with each other, and the prefill valve 22 is closed. When the solenoid of the mold clamping cylinder switching valve 20 is excited, the hydraulic oil is supplied to the cylinder chamber 9 of the mold clamping cylinder 8 so that the mold clamping can be performed.
[0019]
Next, after performing mold clamping and injecting resin to perform foam molding, hydraulic oil is supplied to the boost cylinder 12 in order to move the movable mold 2 in the mold opening direction by a predetermined distance from the mold closing position. The second hydraulic circuit will be described.
[0020]
In FIG. 1, the second hydraulic circuit includes a bidirectional constant displacement hydraulic pump 28. The constant displacement hydraulic pump 28 is driven by a servo motor 30. On the pipe lines extending from the respective discharge ports of the constant displacement hydraulic pump 28, check valves 31 and 32 with pilots are provided. Pipe lines downstream of the check valve 31 with pilot are respectively connected to the cylinder chamber 12a on the mold opening side of the boost cylinder 12, and pipe lines downstream of the check valve 32 with pilot are cylinder chambers on the mold closing side of the boost cylinder 12. 12b. In such a second hydraulic circuit, pipes are assembled so as to be a differential circuit that circulates hydraulic oil in the left and right cylinder chambers 12a and 12b of the boost cylinder. Reference numerals 33 and 34 are check valves for supplying hydraulic oil from the tank to the operating circuit.
[0021]
Next, in FIG. 1, reference numeral 35 is a linear scale. The linear scale 35, the position detection head 36 attached to the moving die plate 4 and the counter 37 are combined to constitute means for detecting the position of the moving mold 2. The output of the counter 37 is introduced into the control unit 38. The control unit 38 is configured by a programmable controller (PLC) or the like, and moves as described below together with a function of switching the above-described switching valve in a predetermined order in order to advance the injection foam molding process according to a pre-set program. A position control circuit for controlling the rotation of the servo motor 30 while feeding back the position of the mold 2 and a servo motor drive circuit are provided.
[0022]
Therefore, the position control in the case of opening the movable mold 2 to the reference position for foam molding by a predetermined amount in accordance with the expansion of the resin by the foaming gas after completing the injection of the resin containing the foaming agent at the time of foam molding will be described. .
The position control of the movable mold 2 is started from the time when the resin injection is completed. First, the control unit 38 places the mold opening / closing switching valve 18 at the neutral position shown in FIG. The cylinder chamber 9 of the clamping cylinder 8 is opened to the drain side by switching to the position shown in FIG.
[0023]
Next, the control unit 38 drives the bidirectional constant displacement hydraulic pump 28 at a predetermined rotational speed by rotating the servo motor 30 in the forward direction at a predetermined rotational speed according to a preset program. Then, a predetermined flow rate of hydraulic oil is introduced into the cylinder chamber 12 a on the mold opening side of the boost cylinder 12. As a result, the movable die plate 4 starts a left line along the tie bar 7. At this time, it is preferable that the flow rate of the working oil is such that the moving mold 2 moves in accordance with the expansion of the resin by the foaming gas generated in the cavity.
[0024]
While the moving mold 2 moves to the reference position set in advance by the program, the position detection signal of the moving mold 2 is fed back from the counter 37 to the control unit 38. And the reference position are compared, and the rotation of the servo motor 30 is continued until the reference position is reached. When the position of the moving mold 2 coincides with the reference position, the control unit 38 sends a stop command to a drive circuit (not shown) of the servo motor 22 to stop the rotation of the servo motor 30. When the moving mold 2 exceeds the reference position, the servo motor 30 may be reversed because the constant displacement hydraulic pump 28 is a bidirectional pump.
[0025]
In this way, the constant displacement hydraulic pump 28 is stopped and the supply of hydraulic oil to the boost cylinder 12 is stopped, so that the movable mold 2 can be stopped at the reference position. In addition, since the constant displacement hydraulic pump 28 is driven by the servo motor 30 and the rotation of the servo motor 30 is controlled while feeding back the position of the moving mold 2, the moving mold 2 can be accurately positioned at the reference position. it can. Furthermore, the hydraulic circuit necessary for position control of the movable mold 2 is a differential circuit in which hydraulic oil circulates from the cylinder opening 12a on the mold opening side of the boost cylinder 12 to the cylinder closing 12b. The constant capacity type hydraulic pump 28 and the servo motor 30 can cope with even a small capacity.
[0026]
Thus, after the moving mold 2 stops at the reference position, the control unit 38 excites the solenoid of the clamping cylinder switching valve 20 to switch the P port to the position where it communicates with the A port. As a result, hydraulic oil from the two hydraulic pumps 14a and 14b is introduced into the cylinder chamber 9 of the mold clamping cylinder 8, and the ram 10 is pressurized against the foaming pressure, so that the movable mold 2 is based on the foaming pressure. Prevent further opening from position. At this time, the mold opening / closing switching valve 18 is switched to the neutral position shown in FIG. 1, the cylinder chamber 12a of the boost cylinder 12 is closed, and the check valve 31 with the pilot and the check valve 33 are operated. Since the oil discharge is blocked, the pressure can be maintained so that the boost cylinder 12 is not moved in the mold closing direction by being pressurized by the mold clamping cylinder 8, so that the mechanical positioning block is conventionally used. It is possible to stabilize the position of the moving mold at the reference position until the foam molding is completed without using the above.
[0027]
Next, FIG. 2 shows a modified example of the boost cylinder. The direction of the boost cylinder 40 is reversed from that in FIG. 1, and the mold is closed when the piston rod 41 is extended, and the mold is opened when the piston rod 41 is retracted. This is an example. A hydraulic circuit similar to that shown in FIG. 1 can be applied.
[0028]
FIG. 3 shows a modification in which the boost cylinder is incorporated in the mold clamping cylinder 8. In this case, a cylinder opening 42 on the mold opening side is formed on the outer periphery of the ram 10, and a cylinder chamber 43 on the mold closing side is formed inside the ram 10.
[0029]
【The invention's effect】
As is apparent from the above description, according to the present invention, the movement and stop of the moving mold can be accurately and stably controlled in accordance with the expansion of the resin by the foaming gas for foam molding, so that the high quality This greatly contributes to the molding of foam molded products with consistent quality.
[Brief description of the drawings]
FIG. 1 is a hydraulic circuit diagram showing an embodiment of a mold opening / closing device of an injection foam molding machine according to the present invention.
FIG. 2 is a cross-sectional view showing a modification of the boost cylinder of the mold opening / closing device of the injection foam molding machine.
FIG. 3 is a cross-sectional view showing another modified example of the boost cylinder of the mold opening / closing device of the injection foam molding machine.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Fixed mold 2 Moving mold 3 Fixed die plate 4 Moving die plate 5 Heating barrel 6 Nozzle 7 Tie bar 8 Clamping cylinder 10 Ram 12 Boost cylinder 18 Mold switching valve 20 Mold clamping cylinder switching valve 22 Prefill valve 24 Prefill valve switching valve 28 Constant displacement hydraulic pump 30 Servo motor 35 Linear scale

Claims (5)

In a hydraulic mold opening and closing device used in an injection foam molding machine for injecting a resin containing a foaming agent into a mold composed of a fixed mold and a movable mold and molding a foam molded product,
A clamping cylinder for applying a clamping force to the mold that has been closed;
A boost cylinder connected to the movable type and moving the movable type;
A hydraulic source is provided, and hydraulic fluid is supplied to and discharged from the mold clamping cylinder and the boost cylinder so that the mold clamping cylinder and the boost cylinder operate in conjunction so as to perform a series of operations for mold opening / closing and mold clamping. A first hydraulic circuit that
A constant displacement hydraulic pump and a servo motor that drives the constant displacement hydraulic pump boost the hydraulic oil to move the movable mold to a foam molding reference position set in the mold opening direction by a predetermined distance from the mold closed position. A second hydraulic circuit for supplying to the cylinder;
Position detecting means for detecting the movable type position;
The position detection means feeds back a position detection signal of the moving type and compares the detected position with the reference position to rotate the servo motor so that the moving type reaches the reference position and is positioned at the reference position. Position feedback control means to control;
First hydraulic circuit switching means for switching the second hydraulic circuit so that supply of pressure oil to the boost cylinder is stopped when the movable type reaches a target position ;
The first hydraulic circuit is switched so that hydraulic pressure in the mold closing direction acts against the foaming force from the mold clamping cylinder to the movable mold and the position of the movable mold is held at the reference position . 2 hydraulic circuit switching means;
A mold opening and closing device for an injection foam molding machine.   The first hydraulic circuit includes a mold clamping switching valve that switches a hydraulic oil flow path to the mold clamping cylinder, and a mold opening / closing three-position switching valve that switches a hydraulic oil flow path to the boost cylinder. The second hydraulic circuit has a differential circuit that circulates hydraulic oil between a cylinder chamber on the mold opening side and a cylinder chamber on the mold closing side of the boost cylinder. Mold opening and closing device for injection foam molding machine.   3. The mold opening / closing device for an injection foam molding machine according to claim 1, wherein the constant displacement hydraulic pump is a bidirectional quantitative hydraulic pump.   3. The mold opening / closing device of an injection foam molding machine according to claim 2, wherein the second hydraulic circuit is a check valve that holds the pressure of the circuit when the quantitative hydraulic pump is stopped.   The mold opening / closing apparatus of an injection foam molding machine according to claim 1, wherein the boost cylinder is incorporated in the mold clamping cylinder.

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