JPH0752202A - Injection mold - Google Patents

Abstract

PURPOSE:To provide an injection mold wherein at the time of injection molding of a molded product possessing a through hole, the product which reduces drastically generation of a warp causing a defective phenomenon, moreover, is superior in molding accuracy, performs automatically gate cutting within the mold and does not leave gate marks behind on the surface can be obtained. CONSTITUTION:A cavity 30 demarcating an external circumferential form of a molded product possessing a through hole is formed between a front mold 11 and rear cavity 14 which is provided contactably and separatably freely on the front mold 11 and along with formation of a gate 31 allowing resin to flow into the cavity 30 from a position of the molded product where a through hole is to form in the front mold 11, a pin 34 which is made freely movable up to the inside of the gate 31 by passing through a part where the through hole of the cavity 30 is to form is provided in the rear cavity 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding die used for molding various resin materials, and particularly, an injection molding die suitable for molding a gear molded product having a through hole in the center thereof. It is about the type.

[0002]

2. Description of the Related Art Generally, when a molded article is injection-molded with a thermoplastic resin or a thermosetting resin, as shown in FIG. 6, a resin melted by heating in a heating cylinder 1 of an injection molding machine is screwed into a screw 2 By filling the cavity 8 from the gate 7 through the sprue 5 and the runner 6 of the injection molding die from the injection nozzle 3.

FIG. 7 shows a mold for molding a circular molded article among conventional injection molding molds (hereinafter abbreviated as molds) used for this type of injection molding. is there. Reference numeral 11 in the figure denotes a fixed-side mold fixed to the fixed-side mounting plate 12. A movable side mold 14 attached to a movable side mounting plate 13 by a spacer block (not shown) is provided on the facing surface side of the fixed side mold 11 so as to be able to come into contact with and separate from the fixed side mold 11. There is. A cavity 15 that defines the outer shape of the circular molded product is formed between the facing surfaces of the fixed-side mold 11 and the movable-side mold 14, and the fixed-side mold 11 is not shown. A sprue 16 and a runner 17 for guiding the molten resin injected from the injection nozzle of the injection molding machine into the cavity 15 are formed. Then, a pinpoint gate 18 having a small diameter is formed between the tip of each runner 17 and the cavity 15 so as to make a gate mark in a molded product inconspicuous. Generally, the pinpoint gate 18 is
In order to speed up the flow of the resin into the cavities 15, it is provided at a plurality of locations 2 to 4 for each cavity 15.

Ejector pins 19 for ejecting the molded product cooled and solidified in the cavity 15 from the cavity 15 are provided in the movable mold 14 so as to be able to move back and forth. The base end is fixed to the ejector plate 20. Then, an ejector rod 21 for projecting the ejector pin 19 through the ejector plate 20 is arranged on the back surface of the ejector plate 20, and between the ejector plate 20 and the movable side mold 14,
A spring 22 for urging the ejector plate 20 toward the movable side mounting plate 13 side is interposed. Reference numeral 23 in the figure denotes a return pin whose base end is fixed to the ejector plate 20.

In order to mold a circular molded product using such a conventional mold, the resin heated and melted from the injection molding machine is passed through the sprue 16 and the runner 17 of the mold from the pinpoint gate 18 ... After filling the cavity 15 and cooling and solidifying, the movable side mold 14 is separated from the fixed side mold 11 to perform mold opening, and then the ejector pin 19 is projected to obtain the above-mentioned molded product.

[0006]

However, in the above-mentioned conventional mold, since the pinpoint gate 18 having a small diameter is used, a considerably high injection pressure is required, which is a burden on the injection device side. Has the drawback that it becomes large. Further, since the flow rate from each pinpoint gate 18 is small, it is difficult to make the resin flow uniform in the cavity 15, and it becomes impossible to obtain sufficient roundness in the molded product, or a distortion that causes a defective phenomenon. Is likely to occur. Furthermore, even if the pinpoint gate 18 is used, it is unavoidable that a gate mark is still left on the surface of the molded product, and it is difficult to cleanly treat the surface.

In addition to the above problems, particularly when a circular molded product having a through hole in the center is molded, for example, the movable mold 14 has the above-mentioned structure as shown by the dotted line in FIG. When the columnar convex portion 25 for forming the through hole is formed, the mold release property of the molded product deteriorates. On the other hand, in order to improve the mold release property of the molded product, the convex portion 25 is tapered. However, if it is formed on the surface of the through hole and a draft is formed, the cylindricity of the through hole deteriorates.

Therefore, as disclosed in Japanese Patent Laid-Open No. 4-369517, the gate is a side gate, and a pressure pin is provided on the side gate so as to move back and forth.
The pressure pin may be used to cut the gate, or the pressure pin may be provided so as to be movable back and forth at a position facing the through hole of the movable mold, and the pressure pin may be projected into the cavity during the molding process. There is also proposed a die in which a pin hole is formed in a molded product, and after the molded product is taken out, a final punching process is performed along the pin hole to form a through hole.
However, even in the above-mentioned mold, although the gate marks are inconspicuous, since it is a side gate, it is difficult to ensure a uniform flow of resin, and after the molding process,
Further, since a secondary processing step such as punching is required to form the through hole, there is a problem that the molding efficiency is reduced.

The present invention has been made to solve various problems of such a conventional mold, and when injection molding a molded product having a through hole, a distortion, which is a defective phenomenon, is significantly generated. It has been reduced to
Moreover, it is an object of the present invention to provide a mold capable of obtaining a molded product without leaving a gate mark on the surface.

[0010]

A mold according to the present invention is a molded product having a through hole between a fixed-side mold and a movable-side mold provided so as to come in contact with and separate from the fixed-side mold. Forming a cavity defining the outer peripheral shape of the mold, and forming a gate in the fixed mold to allow resin to flow into the cavity from the position where the through hole of the molded product is to be formed. It is characterized in that a pin is provided which is capable of advancing and retracting up to the inside of the gate through the portion where the through hole is formed.

The mold is suitable for molding a gear molded product or a circular molded product having a through hole in the center thereof.

[0012]

According to the mold having the above-described structure, the resin can be filled into the cavity and then the pin can be protruded from the cavity into the gate to form the through hole and increase the resin pressure in the cavity. At the same time, gate cutting can be automatically performed in the mold. Therefore, the precision of the molded product can be increased,
Moreover, no gate marks are left on the molded product.

Further, since the gate diameter is large, a large injection pressure is not required, the load on the injection device is reduced, and a uniform resin flow is obtained, so that the molding accuracy can be improved. In addition, since it is possible to correspond to a die for taking a large number of pieces structurally, it becomes possible to form a large number of molded articles of the same precision at the same time.

The above effect is that the gate is arranged in the center of the cavity when the mold is a gear molded product or a circular molded product having a through hole in the center thereof. This is remarkable, and in addition, the effect that the residual stress in the vicinity of the gate of the molded product can be reduced can be obtained.

[0015]

1 to 3 show a mold P of the present invention, which has a through hole H in its central portion as shown in FIGS. 4 and 5.
It shows an embodiment applied to what is molded.
1 and 2, the same components as those shown in FIG. 7 are designated by the same reference numerals and the description thereof will be omitted. In FIG. 1, in this mold, a fixed side mold 1
A plurality of circular cavities 30 (two locations in the drawing) that define the outer shape of the molded product P are formed between the movable mold 1 and the movable mold 14. A gate 31 having a diameter slightly larger than the inner diameter of the through hole H is formed at a position facing the center of each cavity 30 of the fixed mold 11. This gate 31 is a thin film gate,
It communicates with the runner 32 and the sprue 33 which serve as a resin flow path.

On the other hand, at the position facing the gate 31 of the movable mold 14, the pressure pin 34 (pin) passes through the central portion where the through hole H of the cavity 30 is to be formed, and the gate 31 is formed.
It is provided so that it can move back and forth to the inside. The base end of the pressure pin 34 is fixed to the pressure plate 35,
Further, a pressure rod 36 for causing the pressure pin 34 to project into the cavity 30 via the pressure plate 35 is disposed on the back surface of the pressure plate 35. The pressure rod 36 is attached to a pressure cylinder (not shown) for driving the pressure pin 34 forward. When vibrating the pressurizing pin 34, a proportional pressure reducing valve for supplying pressure oil in a pulsed manner into the pressurizing cylinder is connected to the pressurizing cylinder. Incidentally, reference numeral 37 in the figure denotes a spring for urging the pressure plate 35 toward the movable side mounting plate side, and reference numeral 38 denotes
The return pin is shown.

In order to mold a molded product P as shown in FIGS. 4 and 5 with the mold having the above construction, first,
The movable mold 14 is pressed against the fixed mold 11 by the mold clamping device of the injection molding machine to perform mold clamping. Next, the resin melted in the heating cylinder is injected into the mold by the injection device, and the cavity 30 is filled from the gate 31 through the sprue 33 and the runner 32. Then, by further advancing the screw and pushing the resin into the cavity 30, the resin pressure in the cavity 30 is increased.

Next, in this state, the pressure pin 34 is advanced into the cavity 30. Alternatively, the pressure pin 34 is caused to project into the cavity 30 while vibrating. When vibrating the pressure pin 34, as shown in FIG.
After the vibration delay time Td has elapsed, the proportional pressure reducing valve applies a pressure reducing force Δ from the initial exciting force P ₁ to the final exciting force P ₂ to the pressurizing cylinder.
At P, a pulse-like biasing force having an excitation cycle time Tb is applied for the excitation time Ta. Then, the pressurizing pin 34 is oscillated through the pressurizing plate 35 by sequentially repeating a minute forward movement when an urging force acts and a minute backward movement due to the urging force of the spring 37 at the time of decompression. It gradually projects into 30. Along with the protrusion of the pressure pin 34, the resin in the upper portion is extruded into the cavity 30. Incidentally, the vibration of the pressure pin 34 shown in FIG. 3 can be adjusted from once to several tens of times.

Then, as shown in FIG.
Is further advanced, and when the tip portion thereof passes through the cavity 30 and projects into the gate 31 by several tens of μm, a through hole H for the molded product P is formed in the cavity 30 by the pressure pin 34. At the same time, the molding resin in the cavity 30 is completely cut and separated from the resin in the runner 32.

Then, after the cooling time has passed, the movable mold 14 is separated from the fixed mold 11 (mold opening), and the molded product P is ejected from the cavity 30 by the ejector pins 19 ... A molded product P as shown in FIGS. 4 and 5 is taken out of the mold.

According to such a mold, after the resin is filled in the cavity 30, the pressure pin 34 is placed in the cavity 30.
From the inside of the gate 31 to the molded product P
Through hole H can be formed, and at the same time, the resin pressure in the cavity 30 can be increased,
A more accurate molded product can be molded. In addition, since the gate pin can be automatically cut in the mold by the protrusion of the pressure pin 34, a molded product having an excellent appearance can be obtained without leaving a gate mark on the molded product. .

Moreover, since the gate 31 is formed in the central portion of the cavity 30 and the diameter of the gate 31 is larger than that of the conventional one, a large injection pressure is not required and the load of the injection device is reduced. In addition, since a uniform resin flow is obtained in the cavity 30, the molding accuracy can be improved. In addition, since a large stress does not act locally near the gate 31 of the molded product P, it is possible to obtain a molded product P with less residual stress. By the way, since the above-mentioned mold structure can be applied particularly to a mold for taking a large number of molds, a large number of molded products of the same precision can be molded at the same time, which is preferable.

In the above embodiment, the mold for molding the molded product P having the through hole H in the central portion has been described, but the present invention is not limited to this, and as described above, the through hole is formed in the central portion. The same effects can be obtained by applying the present invention to a gear molded product having the above or a molded product having a shape other than the circular shape and the gear shape. Further, although the example in which the pressure pin 34 is used as the pin for forming the through hole and performing the gate cut at the position of the gate 31 has been described, other pins such as an ejector pin may be used instead of the pressure pin 34. Good.

[0024]

As described above, in the mold according to the present invention, the fixed side mold is provided with the gate for allowing the resin to flow into the cavity from the position where the through hole of the molded product is to be formed, and the movable side mold. Since the mold is provided with a pin that can move back and forth to the inside of the gate through the portion where the through hole of the cavity is to be formed, by protruding the pin from the cavity into the gate after filling the resin, the molded product penetrates. Since the holes can be formed and the gate can be cut automatically, no trace of the gate remains on the molded product, and a molded product having an excellent appearance can be obtained. In addition, since the diameter of the gate is large, the load on the injection device is reduced, and a uniform resin flow is obtained, so that the molding accuracy can be improved.

In addition, when the mold is for molding a gear molded product or a circular molded product having a through hole in the central portion, the gate is located in the central portion of the cavity. Further, the above effect is more remarkably obtained, and since a large stress is not locally applied in the vicinity of the gate of the molded product, a molded product with less residual stress can be obtained, which is preferable.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an embodiment of an injection molding die of the present invention.

FIG. 2 is a side sectional view showing a state in which a pressure pin is projected in the mold of FIG.

FIG. 3 is a diagram showing program control for operating a pressure pin in injection molding using the mold of FIG.

FIG. 4 is a side view showing a molded product molded by the mold of FIG.

5 is a front view of the molded product of FIG. 4. FIG.

FIG. 6 is a schematic configuration diagram showing a molding apparatus in which a general mold is incorporated.

FIG. 7 is a side sectional view showing a conventional mold.

[Explanation of symbols]

 11 Fixed Side Mold 14 Movable Side Mold 30 Cavity 31 Gate 34 Pressure Pin (Pin) 35 Pressure Plate 36 Pressure Rod H Through Hole P Molded Product

Claims (2)

[Claims] 1. An injection molding die for molding a molded article having a through hole, wherein a fixed side die and a movable side die provided so as to come in contact with and separate from the fixed side die, Forming a cavity that defines the outer peripheral shape of the molded product, and forming a gate in the fixed-side mold that allows resin to flow into the cavity from a position where a through hole of the molded product is to be formed, and An injection-molding die, characterized in that the movable-side die is provided with a pin that is movable back and forth through the portion of the cavity where the through hole is to be formed and into the gate. 2. The injection molding die according to claim 1, wherein the molded product is a gear molded product or a circular molded product having a through hole in a central portion.