JP2002103385A - Method for manufacturing plastic gear and molding die - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a die structure for molding which shows smooth filling properties when a plastic gear with a disclike metal insert is injection-molded. SOLUTION: The disclike metal insert 1 is inserted into and engaged with a jutting sprue bush 23 formed at the fixed side template, and a gap formed by the insert 1 and a cavity surface 29a formed on the movable side template is used as a disclike gate. Thus a parting line PL is positioned at a most remote spot from the gate, so that air in the cavity can be easily exhausted during injection molding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method of manufacturing a plastic gear having a metal insert at the center and a manufacturing die.

[0002]

2. Description of the Related Art Conventionally, gears manufactured from metal have been sequentially replaced with plastics from small load gears to medium load gears, and recently, the central portion of the gear (hereinafter referred to as the main body side). ) Is made of metal, and metal insert gears made of plastic with a toothed portion and a plastic portion up to a few mm inside diameter have been used for gears with relatively high loads.

[0003] This metal component has a shaft hole at the center thereof to be fitted to the drive shaft, and a thin wall plate capable of withstanding the required strength at an outer diameter portion thereof has a substantially tooth thickness at a diameter portion close to the root diameter. In general, a large number of protrusions are formed on the outer periphery.

When such an insert is inserted into a mold for injection molding and molding is performed, the flow of the molten plastic is restricted depending on the shape of the insert, so that the flow branches off. The disadvantage is that weld lines are generated due to the complicated flow of re-merging and the strength of the molded product is insufficient, or the air in the cavity is difficult to be discharged to the outside, so that rapid filling cannot be performed and the molding cycle becomes longer. was there.

Usually, a cavity of an injection molding die has a cavity formed in a fixed mold plate, and a core is formed in a movable mold plate. When injection molding is performed, molten plastic shrinks with cooling and the core is formed. And ejected out of the mold by an ejector pin which stays at a fixed position during the mold opening process. For example, in the gear molding die having the insert shown in FIG. 7, the insert 1 is mounted in the cavity of the movable mold plate to serve as a core, and the molten plastic is formed by the insert and the fixed mold plate. The cavity is filled through a channel provided between the cavity and the surface, and comes into close contact with the core which is an insert. Therefore, when the mold is opened, it is retracted together with the movable mold plate and released by the protruding pins 27. This is a general mold structure.

In a gear mold as shown in FIG. 7 in which the metal insert occupies most of the space in the cavity and the space filled with the molten plastic is extremely narrow and far away, a large injection is required to fill the molten plastic. Since (filling) pressure is required, the amount of shrinkage of the filled plastic is also reduced, so that the ejection resistance of the molded product by the ejector pins 27 becomes very large. In order to cope with this, an ejector pin is installed at a position including a boundary between the insert and the filled plastic (P in FIG. 7), and the molded product is removed from the mold mainly depending on the rigidity of the metal insert. To be discharged.

[0007] When filling the mold cavity with the molten plastic, the air in the cavity and the gas emitted from the plastic are compressed in the cavity and hinder the flow of the molten plastic. In order to cope with this, it is necessary to adjust the position of the parting line PL of the mold in the cavity, provide an air vent, or connect the cavity and the vacuum chamber when the mold is closed to make the inside of the cavity vacuum. It has been done.

Since the cavity is formed in the movable mold plate from the insertion of the insert in the gear insert molding die shown in FIG. 7 and the arrangement of the ejector pins, the fixed mold plate and the movable mold plate are formed. Is at a position deviated toward the injection side with respect to the cavity. Therefore, when this mold is filled with molten plastic, air and the like in the cavity are partially discharged by the parting line, but when the molten plastic passes through the parting line, air cannot be discharged. The pressure inside the cavity becomes high, and it is necessary to increase the injection pressure for filling. As a result, the time until the filling is completed also increases.

To cope with such a problem, a vacuum chamber is connected to the cavity via a degassing path, as described above. However, not only the equipment cost is increased, but also the timing adjustment of mold clamping and evacuation is slightly performed. This is a difficult operation, and there is a problem that plastic enters the deaeration path (air vent).

[0010]

[0005] Such a metal insert is inserted into a mold, and the outer periphery of the metal insert, that is, a tooth or a portion forming the tooth is filled with molten plastic by an injection molding machine. However, depending on how the metal insert is held in the mold, the position of the parting line of the mold, and the position of the gate for filling the plastic, etc., the molding efficiency and quality of the molded product are greatly affected. Is generated.

That is, if the holding mechanism of the insert is poor, the insert will drop at the stage of closing the mold and the mold will be damaged. The position of the parting line affects the operability of attaching / detaching the insert, and the air in the mold cavity and the gas from the molten resin cannot be exhausted sufficiently outside the mold due to the position of the gate. Inhibits molding efficiency. Also, depending on the position of the gate, a clear weld line is generated in the molded product, and the strength is impaired.

According to the present invention, in a mold for inserting an insert having an influence on the flow of a molten resin, the molding efficiency can be improved by setting the position of a gate and a parting line capable of obtaining a reasonable flow of the resin. To improve the quality of molded products.

[0013]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to an injection molding die for molding a plastic gear whose main body is made of a metal insert.
A structure in which a sprue bushing having a diameter that is inserted into a shaft hole formed in the center of an insert and having a subtle gate hole in the center of the fixed side template is projected toward the cavity surface of the movable side template in the fixed side template. When the mold is opened, the insert is inserted and held in the sprue bush, then the mold is closed, and molten plastic is injected into the cavity of the mold to be molded. We aimed for safe, high-speed molding without falling down.

[0014] Further, the fixed side mold plate holding the insert by inserting a shaft hole of the insert into the core by protruding the core having the sblue gate (or nozzle) hole is formed as a cavity. The cavity which is compressed by the molten plastic injected from the injection molding machine has no concave amount at all, or is not more than 2 mm, and has a concave as a cavity formed in the movable mold plate which is paired with the cavity. The inside air can be easily discharged from the parting line PL to the outside.

Further, in a metal mold for forming a thick portion or a tooth profile for forming a tooth profile on an outer peripheral portion of the metal insert by injection molding, the molten plastic is formed by diametrically extending one side surface of the insert from a center of the insert. The fluid structure was such that it flowed while expanding into a shape, and then filled into a thick portion or a tooth portion. In this way, by forming the gate on one side of the entire surface of the insert, the generation of weld lines in the tooth profile is prevented.

[0016]

Embodiments of the present invention will be described with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS The drawings show an embodiment of the present invention. FIG. 1 is a side view showing a metal insert gear according to the present invention in a half section, and FIG. 2 shows a metal insert in a half section. FIG. 3 is a central vertical sectional view showing a main part of an injection molding die, and FIG. 4 is a plan view showing a cross section of a relation between a metal insert and a molded tooth profile. 5 is a front view showing a cross section of the insert molding die according to the present invention, FIG. 6 is a plan view of a movable mold plate showing a cavity portion, and FIG. 7 is a front view showing a conventional insert die. is there.

In this embodiment, the gear 10 is formed of metal from the shaft hole portion 1a to the vicinity of the base of the tooth profile (hereinafter, referred to as the main body portion of the gear or the insert).
The tooth profile is made of plastic. As shown in FIG. 2, the main body portion of the gear 10, that is, the insert 1
Is approximately the same as the required gear thickness,
In addition, a number of small protrusions 1c for preventing slippage are formed on the outer periphery 1b regardless of the number of teeth formed of plastic, and a shaft hole which fits with the outer diameter of a sprue bush 23 described later at the center thereof. 1a is opened. It is usual, but not essential, that a groove 1d be formed around one side surface between the shaft hole 1a and the outer periphery 1b to reduce the weight.

As shown in FIG. 5, a mold 20 for molding the plastic gear 10 with an injection molding machine has a sprue gate hole 23a at the center of a fixed side mold plate 22 attached to a fixed side attachment plate 21. The opened sprue bush 23 is fitted and inserted so as to project toward the movable mold plate. The mold plate 22 has no cavity as a cavity, or a depression (cavity) 22a corresponding to an inclined or rounded portion for forming a slight chamfer at the edge of the molded product has a slight depth. Is formed. It is desirable that the depth of the depression is 2 mm or less at the maximum.

On the other hand, the movable-side mounting plate 25 is mounted on the movable-side mold plate 28 via a spacer block 26 and a receiving plate (not shown). Is installed. The movable-side mold plate 28 is opposed to the fixed-side mold plate 22 and the sprue bush 23 inserted in the protruding shape when the mold is closed.
A gap (2 mm or more, desirably 3 to 8 mm) where the tips of the inserts do not come into contact with each other, and the insert 1
A cavity 29 having a sufficient space for forming a plastic thick portion (10a in FIG. 1, 29b in FIG. 5) having a height equal to or greater than the tooth diameter of the outer diameter is formed.
A slug well 29w is formed on the surface of the cavity 29a facing the tip of the sprue bush 23, and a pressure receiving ring 24 prevents deformation of the insert.

FIG. 6 is a plan view showing the shape of the cavity 29 and the arrangement of the ejector pins.
Is shown as a smooth circumference, but may be formed in a required shape (shown by phantom lines). Needless to say, when the shape is formed as a smooth circumference as shown by the solid line in FIG. 6, a further gear cutting step using a gear cutting machine is required after plastic injection molding. In this figure, 28a is a guide pin or a guide hole of the guide pin.

In such a cavity 29 of the mold of the present invention, the insert 1 has its shaft hole 1a inserted into the fixed mold plate 2.
After being inserted into and held by the sprue bush 23 protruding from the side 2, the mold is closed by moving the movable mold plate 22 forward by operating the injection molding machine, and then melting the polyamide or polyacetal through the sprue gate hole 23a. The cavity 29 is filled with engineering plastic.
The molten plastic injected from the sprue hole 23a through the nozzle of the molding machine is injected into one of the inserts 1, that is, a gap sandwiched between the movable side surface of the molding machine and the movable cavity surface 29a. Further, the molten plastic to be filled proceeds while expanding the flow front in the gap into a disk shape and reaches the outermost diameter portion, that is, the side surface of the thick portion 29b for forming the tooth profile or the tooth profile. Instead, the fluid flows into the tooth profile 29c or the thick portion 29b for forming the tooth profile, and the filling of the cavity 29 is completed.

As the molten plastic flows in the cavity 29, the air in the cavity is pushed to the tip of the flow of the molten resin and compressed toward the farthest position from the sprue gate. It is necessary to provide a vent or a parting line as a so-called gas vent at the farthest position. However, in the present mold, since the cavity 22a is hardly recessed in the fixed mold plate 22, the movable mold is provided. The parting line (surface) PL where the fixed mold plates face each other is the final end of the flow path of the molten plastic. Therefore, the air in the cavity 29 and the gas emitted from the molten plastic are easily discharged into the atmosphere from the parting line PL. Although not shown, several narrow grooves having a depth of 0.05 to 0.1 mm are formed as air vents on the parting line surface from the edge of the cavity 29 to the end surface of the template 28. Is, of course, desirable.

In the case of the mold having this structure, the position of the ejector pin 27 from which the molded product is to be projected out of the mold is, of course, the filled plastic surface (all of the surfaces are paths for molten plastic and are covered with plastic). Exhausted)
When the mold is opened and the molded product is ejected in a state where the cooling is not sufficiently performed, the portion is deformed by the pressure of the pin 27, or the tip of the pin is immersed in the molded product and the pin and the molded product Is difficult to release from the mold. As a countermeasure, in the mold according to the present invention, the diameter of the ejector pin is made 12 mm or more, which is larger than that in a normal mold, so that the pin is not immersed. The pin 27 was arranged at the portion.

Injection molding is performed by the above-described operation, and the formed insert gear 1 has one side surface of the insert, that is, the molten plastic, if the necessary tooth profile 9c is formed on the inner periphery of the cavity 29. The plastic portion of the passage portion 5a and the slug well 5w (FIGS. 1 and 3) attached to the passage side and the side surface of the tooth profile are scraped off to complete the gear shown in FIG.

Further, the necessary tooth profile is not formed on the inner peripheral surface of the cavity 29, and the plastic is formed by a cavity having a smooth circumferential surface as the tooth length plus a small amount of the thick portion 29b. In this case, the unnecessary plastic portion 5a on the side surface is scraped off in the same manner as described above, and then the thick portion 10a is cut by a machine tool such as a gear cutting machine to process the tooth profile 10b. The gear 10b formed by this operation can easily obtain a gear having better dimensional accuracy than the tooth profile formed by the cavity 29c.

[0026]

According to the present invention, in a gear molding die for inserting a metal insert, a core for inserting the insert into a stationary mold plate is protruded, and a sprue gate hole is opened at the center of the core to melt the plastic. It has a structure in which it flows into the thick part for tooth profile or tooth profile cutting through the gap formed by the bottom surface of the cavity and the insert, and the fixed mold has no cavity as a cavity, or By setting the depression amount to 2 mm or less, the exhaust of air and gas accompanying the flow of the molten plastic was facilitated, and the molding efficiency and the quality of the molded product were improved.

[0027] The better venting has reduced the injection molding pressure required for filling the molten plastic, and has enabled the use of smaller molding machines, thereby preventing deformation of the insert.

By forming the gap between the bottom surface of the cavity and the insert sufficiently thick, the flow resistance of the molten plastic at the time of injection molding is reduced, and low pressure molding becomes possible, and therefore, the residual stress in the molded product is reduced. Deformation and distortion hardly occurred.

[Brief description of the drawings]

FIG. 1 is a side view, partially in section, showing a finished product of an insert gear according to the present invention.

FIG. 2 is a side view, partially in section, showing a metallic insert.

FIG. 3 is a cross-sectional plan view partially showing a relationship between a small protrusion formed on a metallic insert and a tooth mold formed of plastic.

FIG. 4 is a side view of an insert gear formed by a mold according to the present invention, and a part thereof is shown in a cross section.

FIG. 5 is a central sectional view showing an outline of a mold according to the present invention, in which inserts are indicated by imaginary lines and flow paths of molten plastic are indicated by solid arrows.

FIG. 6 is a plan view showing a cavity surface formed on the movable mold plate of the mold according to the present invention, and shows tooth shapes formed on the inner peripheral surface of the cavity by imaginary lines.

FIG. 7 is a partial cross-sectional side view showing an outline of an insert molding method according to a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insert object 10 Plastic gear 20 Die 21 Fixed side mounting plate 22 Fixed side type plate 23 Sprue bush 24 Pressure receiving ring 25 Movable side mounting plate 26 Spacer block 27 Ejector pin 28 Movable side type plate 29 Cavity of sufficient space

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Eiji Hayashi 5-1-1, Higashi-Mikunigaokacho, Sakai-shi, Osaka Daiwa Gosei Co., Ltd. F-term (reference) 3J030 AC03 BA01 BC01 BC02 BC08 4F202 AD03 AH12 CA11 CB01 CB12 CK02 CK41 CQ05 4F206 AD03 AH12 JA07 JB12 JQ81 JW23

Claims (3)

[Claims] 1. An injection molding die for inserting a metal insert in advance and molding a plastic tooth profile on the outer periphery thereof, wherein the fixed side mold plate has a diameter inserted through a shaft hole formed at the center of the insert. The sprue bush with a sprue gate hole at its center is projected to the movable mold plate side, and when the mold is opened, an insert is inserted through the sprue bush and held to close the mold. A method of manufacturing a plastic gear, comprising injecting and molding into a cavity mainly formed in a movable mold plate. 2. A fixed-side mold plate for holding an insert by making a sprue bush having a sprue gate hole protrude toward the movable mold plate side and fitting the shaft hole of the insert into the sprue bush. A mold for manufacturing a plastic gear, characterized in that the mold has no dent amount at all, or the dent amount is 2 mm or less, and therefore most of the dents as cavities are formed in the movable mold plate. 3. A plastic injection molding die for forming a thick portion or a tooth profile for forming a plastic tooth profile on an outer peripheral portion of a metal insert previously inserted into the die, wherein the molten metal is injected into a cavity through a sprue bush. The plastic is characterized in that it is the entire surface of the gap between the insert and the cavity surface formed in the movable mold plate as a flow path (gate) to the thick portion or the tooth portion for forming the tooth profile. The gear molding die according to claim 1 or 2.