JPH0355291B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an injection molding machine that can prevent overfilling after resin filling is completed in injection molding.

(Prior art) In general, the injection process includes a filling process from the start of injection until the resin almost fills the mold, a compression process to compress the resin filled in the mold, and a process to compress the compressed and filled molten resin. Control is performed by dividing into pressure holding processes, such as to compensate for shrinkage due to cooling or to stop backflow of resin in the product part.

Specifically, the injection speed is controlled by controlling the speed of the injection screw or injection plunger in the filling process (injection speed control area), and by controlling the injection cylinder hydraulic pressure in the compression process and pressure holding process (injection pressure control area). This is done through control.

Switching from the injection speed control area to the injection pressure control area is performed after confirming completion of filling based on changes in the position of the injection plunger, the oil pressure in the injection cylinder, or the resin pressure in the cavity.

(Problems to be Solved by the Invention) However, in the above method, when switching from confirmation of resin filling completion to injection pressure control, there is a delay in the response of the control system, and the movement of movable parts such as the injection plunger or injection screw is delayed. The injection plunger overruns due to inertia, making accurate control difficult. In addition, the mold may be overfilled with resin, causing burrs on the product, which has been a problem.

To solve this problem, it is possible to slightly advance the switching timing in anticipation of the overrun of the injection plunger, but since the resin pressure in each part increases as filling is completed, the filling completion point can be determined by resin pressure or hydraulic pressure. With the control method being tested, it was difficult to determine the switching timing before filling was completed.
Further, even if the injection plunger is switched at the forward position, the forward position changes depending on the molding conditions for each cycle, so it is difficult to set the position accurately.

Therefore, in view of the above circumstances, an object of the present invention is to
It is an object of the present invention to provide an injection molding machine that can prevent the occurrence of burrs on molded products due to overfilling of resin after filling due to delay in response of a control system, inertia of movable parts, etc.

(Means for Solving the Problems) The present inventor has proposed that in order to prevent the occurrence of burrs on the molded product due to the above-mentioned overfilling, when the filling of the resin into the cavity is completed, the resin is guided into the cavity. It has been found that it is effective to increase the volume of the resin passage to absorb overfilled resin.

Furthermore, the inventor has developed a method for increasing the volume of the resin path in the runner section formed on the parting surface of the mold, where the resin cooled and solidified inside is released from the mold and discharged outside the mold when the mold is opened. Providing this section allows the resin that has flowed into the volume increasing section to be cooled and solidified, and together with the resin in the runner section, is easily released from the mold and discharged from the mold when the mold is opened. The present invention was developed based on the knowledge that troubles caused by the deterioration of the inflowing resin can be avoided.

That is, in the first aspect of the present invention, the resin injected from the injection plunger is inserted into the resin path so as to coincide with the wall surface of the runner portion formed on the parting surface of the molding die. A pressure sensor that detects the resin pressure in the resin path or cavity is installed so that the end face of the cylinder rod that can move forward and backward in the mold is exposed, and the volume of the runner section is increased when the resin filling into the cavity is completed. drive means for moving the cylinder rod in a direction backward with respect to the runner section based on the detection signal of the pressure sensor so that the pressure detected by the pressure sensor becomes equal to the appropriate pressure in the resin path or the cavity; An injection molding machine is characterized in that it is provided with.

Further, the second aspect of the present invention is such that the resin injected from the injection plunger is arranged so that the resin path to the cavity coincides with the wall surface of the runner portion formed on the parting surface of the molding die. The tip of the cylinder rod, which is movable in the mold, is exposed, and when the resin filling into the cavity is completed, the cylinder rod is moved back relative to the runner part to increase the volume of the runner part and maintain the appropriate pressure in the cavity. In the injection molding machine, the back pressure on the cylinder side of the cylinder rod is set to be equal to the appropriate pressure in the resin passage when filling the cavity with resin is completed.

(effect) Next, the operation of this invention will be described.

When switching from the injection speed control area to the injection pressure control area, if the pressure inside the cavity or the resin path connected to the cavity becomes higher than the appropriate pressure due to overfilling of resin, one part of the resin path The cylinder rod whose tip end face is aligned with the wall surface constituting the runner section moves back, increasing the volume of the runner section and absorbing the overfilled resin.

Therefore, it is possible to prevent the injection plunger from overrunning due to a delay in response of the control system, inertia of the movable part of the injection molding machine, etc., and the generation of burrs on the molded product due to overfilling of the cavity with resin.

In addition, since the volume increasing part is formed in the runner part formed on the parting surface of the mold, the resin that has flowed into the volume increasing part is cooled and solidified when the mold is opened, and the resin flows into the runner part. Since it is released from the mold together with the resin and discharged from the mold, it is also possible to avoid troubles caused by deterioration of the resin that has flowed into the volume-increasing portion.

(Embodiments) Hereinafter, preferred embodiments of the present invention will be described in detail based on the accompanying drawings.

[First Embodiment] FIG. 1 is a longitudinal sectional side view showing a molding die portion of an injection molding machine according to the present invention.

Molding molds designated by reference numeral 10 are fixed to the inner surfaces of a fixed platen 22 and a movable platen 24 in an injection molding machine 20, respectively.

The injection molding machine 20 is, for example, an in-line screw type injection molding machine in which a screw serving as an injection plunger is inserted into an injection cylinder, and an injection nozzle 26 provided at the front end of the injection cylinder is shown. An injection ram (not shown) is provided at the rear end of the injection cylinder.

Further, the movable platen 24 is guided by tie bars 28 relative to the fixed platen 22, and opens and closes the mold by a mold clamping device (not shown).

On the other hand, the molding die 10 has a movable die 10a and a fixed die 1.
The movable mold 10a is fixed to a movable platen 24, and the fixed mold 10b is fixed to a fixed platen 22.

A cavity 12, a gate portion 14, and a runner portion 16 are carved on the parting surfaces of the fixed mold 10b and the movable mold 10a, respectively, and a sprue portion 18 is provided on the fixed mold 10b following the runner portion 16. Resin injected from an injection cylinder (not shown) is then injected into the cavity 12 through the injection nozzle 26 , the resin path 30 formed by the sprue section 18 and the runner section 16 , and the gate section 14 .

A cylinder 3 serving as a driving means is provided in the movable mold 10a.
2 is provided, and a piston 3 within this cylinder 32
4, one end of a cylinder rod 36 is connected to the cylinder rod 36 so as to be movable forward and backward in the mold opening/closing direction.

The other end surface of the cylinder rod 36 is
It faces so as to coincide with the wall surface of each runner section 16 that constitutes a part of the resin path 30.

Additionally, a sensor rod 38a is installed in the cavity 12.
is connected to the pressure sensor 38. Then, the driving means is appropriately driven by the detection signal from the pressure sensor 38, and the cylinder rod 36 is moved backward so that the volume of the runner section 16 is increased.

Next, the operation of this embodiment will be explained.

(1) The movable mold 10a is moved forward and clamped by the mold clamping device.

(2) Inject by bringing the injection nozzle 26 into contact with the fixed mold 10b (state in Fig. 1).

(3) Filling of the resin into the cavity 12 is completed,
When all the pressure sensors 38 detect that the internal pressure of the cavity 12 has increased to a preset pressure, the cylinder 32 is controlled by the signal, and the piston 34 is retracted (state in FIG. 2).

(4) As a result, the volume of the runner portion 16 (resin passage 30) increases by the amount that the cylinder rod 36 has retreated.

(5) At the same time, switch injection control to pressure control.

(6) Then, even if the injection plunger overruns due to the response delay of the control system during switching or the inertia of the movable parts of the injection molding machine, the resulting pressure increase will result in an increase in the volume of the runner section 16 (resin path 30). Absorbed by minutes.

(7) After that, the molded product is cooled and solidified under pressure control, and then the mold is opened and the molded product is taken out.

Note that when the cylinder rod 36 retreats, some of the resin from the runner section 16 flows into this retreated space, but since this flowing resin can be discharged in the mold opening/closing direction, it is easily released from the mold together with the resin from the runner section 16. .

In this embodiment, the switching to the pressure control region was performed simultaneously with the operation of the cylinder 32 by the internal pressure of the cavity 12, but only the cylinder 32 was operated by the internal pressure of the cavity 12, and the switching to the pressure region was performed by changing the screw position. You can go.

Further, in this embodiment, one pressure sensor 38 is provided for each cavity 12, and when all the pressure sensors 38 exceed the set pressure, the cylinder 32
However, since the purpose is to confirm the filling of the cavity 12 where resin is injected last, it is sufficient to provide only one in the cavity 12 where resin is injected last. .

[Second Example] Next, a second example shown in FIG. 3 will be described.

The second embodiment will be described using the same reference numerals for the same parts as those in the first embodiment.

A cavity 12, a gate portion 14, a runner portion 16, and a sprue portion 18 are formed in the molding die 10.

Further, a cylinder 32 is provided within the movable mold 10a, and a piston 3 that reciprocates within this cylinder 32.
4 is followed by a cylinder rod 36. The tip of this cylinder rod 36 faces the runner section 16.

Then, the back pressure of the piston 36 is
Runner part 16 when filling of resin into 2 is completed
It is configured so that the pressure can be set equal to the appropriate pressure within.

The rest of the structure of this embodiment is similar to that of the first embodiment, but this embodiment does not include a pressure sensor. Therefore, in this embodiment, the cylinder 32 itself operates by sensing the pressure in the runner section 16, and also serves as a pressure sensor.

In other respects, the same operations and effects as in the first embodiment are achieved. Also, since the cylinder rod advances and retreats in the same direction as the mold opening/closing direction of the mold, the cylinder rod 3
The resin that has flowed into the space where 6 has retreated is the runner part 16
It is easily released from the mold along with the resin.

Although the present invention has been variously described above with reference to preferred embodiments, it goes without saying that the present invention is not limited to these embodiments and can be modified in many ways without departing from the spirit of the invention.

(Effects of the Invention) Since the present invention is configured as described above, it produces remarkable effects as shown below.

In the present invention, even if there is a delay in the response of the control system when switching from the injection speed control area to the injection pressure control area, or if the injection plunger overruns due to the inertia of the movable parts of the injection molding machine, the resin pressure in the cavity increases. The cylinder rod facing the runner section can be moved back to adjust the pressure so that no pressure is applied. Furthermore, since the resin pressure within the cavity does not increase, burrs do not occur on the molded product.

Because the tip of the cylinder rod faces the runner, resin pressure can be adjusted close to the cavity, resulting in quick response.

Facing the runner section, the cylinder rod advances and retreats in the same direction as the opening and closing direction of the mold, so that the resin that has flowed into the space where the cylinder rod has retreated is easily released from the mold together with the resin in the runner section.

Since the volume within the cavity does not expand, the volume within the cavity does not change, and no extra protrusions of resin are formed on the surface of the molded product.

[Brief explanation of drawings]

The drawings show preferred embodiments of the present invention, and FIGS. 1 to 3 are longitudinal sectional side views showing a mold portion of an injection molding machine. 10...Molding mold, 12...Cavity, 16
... Runner section, 20 ... Injection molding machine, 22 ... Fixed plate, 24 ... Movable plate, 30 ... Resin path, 32 ...
...Cylinder, 36...Cylinder rod, 38...
Pressure sensor, 38a...sensor rod.

Claims (1)

[Scope of Claims] 1. The resin injected from the injection plunger is placed within the mold so that the resin path to the cavity coincides with the wall surface of the runner portion formed on the parting surface of the mold. A pressure sensor that detects the resin pressure in the resin path or the cavity is installed so that the end face of the cylinder rod that can move forward and backward is exposed, and when the resin filling into the cavity is completed,
The cylinder rod is retreated relative to the runner section in response to the detection signal of the pressure sensor so that the volume of the runner section is increased so that the pressure detected by the pressure sensor is equal to the appropriate pressure in the resin path or cavity. An injection molding machine characterized by being provided with a drive means for moving in the direction. 2. A cylinder rod that is movable in the mold so as to be aligned with the wall surface of the runner section formed on the parting surface of the mold, in the resin path through which the resin injected from the injection plunger reaches the cavity. The cylinder side of the cylinder rod is facing so that when the filling of the resin into the cavity is completed, the cylinder rod is retracted from the runner part to increase the volume of the runner part and maintain the appropriate pressure in the cavity. An injection molding machine characterized in that the back pressure is set to be equal to the appropriate pressure in the resin passage when filling the resin into the cavity is completed.