JPH1024454A - Gear mold and manufacture of gear - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rapidly fill a mold with a resin, to obtain excellent tooth-shape transfer properties and to perform accurate molding even when an elongated gear with an L/D ratio of 0.7 or more is molded from a resin having an inferior flowability in a case molding a gear from a resin. SOLUTION: A movable template 1 having a tooth form mold 1a of a gear and the core pin 1b protruding from the center of the end surface on the moving side of the mold 1a toward the fixed side thereof and the fixed template 2 opposed to the movable template 1 and the core pin 2b coaxial to the core pin 1b to protrude toward a movable mold and the resin supply passage 2c piercing the core pin 2b to be opened to the leading end of the core pin 2b are provided. At a time of mold clamping, the core pins 1b, 2b are coaxially arranged in the tooth form mold 1a to form a gap 3 for a disk gate between the leading end surfaces of the core pins 1b, 2b opposed to each other at the center in an axial direction. A resin is filled into a hermetically closed space from the disk gate to be cooled and solidified and, after a runner is separated from the disk gate part 3, a molded product is ejected from a mold and the disk remaining on the inner periphery of the molded product is removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gear forming die and a method for manufacturing a gear.

[0002]

2. Description of the Related Art As a molding die for a plastic product, a movable die B incorporating a core pin A as shown in FIG. 7 is pressed against a fixed die C to close the die, and a resin D is introduced into a closed space from a pinpoint gate E. Injection molds for injection filling are known. By the way, this molding die is provided with a pinpoint gate E at the end of the cavity, and the molten resin supplied from the gate E goes through the cavity and meets again at the end of filling. In some cases, insufficient transfer to the substrate or weld marks may occur.

[0003] In particular, in the case of a resin having a high melting temperature and poor fluidity, such as a polyimiamide (PAI) having excellent heat resistance and body loadability, the above-mentioned drawbacks are likely to occur. Insufficient transfer of the tooth profile and the formation of weld marks reduce the accuracy of molding such as the outer diameter and runout of the product, as well as the physical properties of the product. The accuracy is low and the engagement is poor, and there is a problem that when used in a place where the driving accuracy is required in an electrophotographic apparatus such as a printer, a facsimile or a copying machine, an adverse effect such as image blur occurs.

[0004] Therefore, when gears or the like that require particularly high precision are injection-molded, disk gates that hardly cause weld marks are often used. As shown in FIG. 8, a fixed die C having a sprue portion F and a core pin A having an inner peripheral surface of a gear with respect to the fixed die C are coaxially opposed to the sprue F as shown in FIG. And an insert B having a gear tooth profile concentrically outside the core pin A.
There is known a disk gate type injection molding die comprising a movable die B which can be pressed into contact with the fixed die C in which the fixed die ₁ is disposed.

[0005]

However, in the disk gate type mold shown in FIG. 8, the injection resin is a protrusion A on the end face of the core pin A.
After colliding with ₁ , the cavity is filled from the disc gate E ₁ located at the end of the cavity B _2, so that the distance to the mold end opposite to the disc gate E ₁ is long, and the above-mentioned polyimide amide (PAI) In the case of such a resin, the disadvantage that the tooth profile of the mold cavity is not sufficiently transferred to the filled resin remains. In particular, there is a problem that the above-mentioned disadvantage becomes more remarkable as the ratio of the length L to the outer diameter D of the elongated gear becomes 0.7 or more.

[0006]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention is intended to quickly fill a resin into a mold even when an elongated gear having an L / D of 0.7 or more is formed of a resin having poor fluidity. It is an object of the present invention to obtain a gear forming die and a method of manufacturing a gear that can be formed with excellent tooth profile transferability and high precision.

[0007]

That is, a gear forming die according to claim 1 has a gear tooth mold 1a and a core pin 1b protruding toward the fixed side from the center of the moving end surface of the mold 1a. A side mold plate 1, a core pin 2 b facing the movable side mold plate 1 and coaxial with the core pin 1 b and protruding toward the movable mold, and a resin supply passage 2 c penetrating through the core pin 2 b and opening at the tip of the core pin 2 b. When the mold is closed, the core pins 1b and 2b are coaxially aligned in the tooth form mold 1a and are disposed between the end faces of the core pins 1b and 2b facing each other at the axial center. Gap 3 for gate
Is formed.

According to a second aspect of the present invention, there is provided a gear molding die according to the first aspect, wherein the tooth mold 1a of the movable side mold plate 1 is housed as the outer case 1c, and the core pin 1b is provided with the core pin 1b. When it is fitted concentrically with the outer nest 1c, it becomes an inner nest 1d, and is rotatable around a gear shaft on which the outer nest 1c is formed.

According to a third aspect of the present invention, there is provided a method of manufacturing a gear, comprising closing a gear forming mold according to the first and second aspects, and injecting the molten resin through the sprue S, the runner R, and the resin supply path 2c to the core pin 1b. And a gear forming step of filling and cooling and solidifying the sealed space from the disk gate 3 formed on the front end opposing surface of the and 2b, and after separating the movable mold 1 from the fixed mold 2 and separating the runner at the disk gate 3 portion, It is characterized by comprising a demolding step of projecting the molded article G from the mold and a gate removing step of removing the disk 3a remaining on the inner periphery of the molded article G.

[0010]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a sectional view showing a closed state of a gear molding die according to the present invention. The gear molding die includes a tooth mold 1a forming a closed space for gear molding and a moving side of the mold 1a. A movable mold plate 1 having a core pin 1b protruding toward the fixed side from the center of the end face; a core pin 2b opposed to the movable mold plate 1 and concentric with the core pin 1b and protruding toward the movable side; A fixed-side mold plate 2 having a tapered conical resin supply passage 2C that penetrates through the inside of the core pin 2b and opens at the tip of the core pin 2b.

The movable template 1 is fixed to the fixed template 2.
When the mold is closed in contact with the mold, a gap 3 for a disc gate is formed at the front end faces of the core pins 1b and 2b which are coaxially aligned in the mold 1a. This gap
The cross-sectional shape of the disk gate 3 is set to be substantially constant in thickness as a whole, and the core pin 1b or 2b or both opposing surfaces are formed as recessed surfaces so that the disk gate 3 can be closed to the gear molding enclosed space. Can be made thinner than the gap at the center. Then, the molten resin is supplied from the injection nozzle through the runner R, the resin supply path 2c, and the disc gate 3 into the tooth mold 1a forming the gear molding closed space.

In the above description, the movable mold comprises the movable mold plate 1, the receiving plate 4 supporting the core pin 1b, the spacer 5, the movable mounting plate 6, the eject pin 7, and the eject plates 8a and 8b supporting the eject pin 7. It is composed of The fixed mold includes the fixed mold plate 2, a runner strip plate 9 that forms a runner R at a parting surface with the fixed mold plate 2, a fixed mounting plate 10, and a locate ring 11. The molten resin is injected and supplied from the installed injection molding nozzle 12.

A plurality of tooth molds 1a... 1a are radially provided in one movable mold 2 around an injection molding nozzle so that a large number of gears can be simultaneously molded in the gear molding die.

Although not shown, the moving-side mounting plate 6 is fixed to a die plate of an injection molding machine, and slides back and forth in the axial direction of the injection molding machine together with the die plate to perform mold clamping and mold flat wood. Will be Further, a stopper device for controlling the stop positions of the fixed side mold plate 2 and the runner strip plate 9 when the mold is flat is provided on the side surface of the mold.

FIG. 2 is an enlarged view of a main part of the gear forming mold shown in FIG. 1, and shows a tooth profile of the movable mold plate 1 when a gear having an inclination angle with respect to an axis of a helical gear or the like is formed and demolded. The mold 1a is smoothly rotated along the tooth streaks. That is, the tooth mold 1a of the movable side template 1 is
The outer pin 1c and the core pin 1b are fitted into the inner pin 1d concentrically with the outer pin 1c, and are rotatable about a gear shaft on which the outer pin 1c is formed. I have.

In the above, the outer case 1c having the tooth form mold 1a is attached to the board of the movable side mold plate 1 via the bearing 1e, and the flange portion 1f does not come off from the movable side mold plate 1 when the mold is removed. Is provided. In addition, nested child 1d
Are eject pins 7, 7 concentrically arranged inside the outer nest 1c via the bearing 1e 'and projecting the product to the inner nest 1d.
Is provided.

Next, a method of manufacturing a gear according to the present invention will be described. As shown in FIG. 1, the molten resin injected into the closed mold is supplied from the sprue S to the runner R, through the tapered conical resin supply path 2c, and from the disc gate 3 to between the tooth mold 1a and the core pins 1b, 2b. It is filled in the formed gear molding closed space. At this time, the resin spreads radially at the disk gate 3 located substantially at the center of the gear thickness (length in the axial direction) and fills the enclosed space for forming a gear. The distance is short and no weld occurs.

After the molten resin is cured after injection filling, it is released from the mold at the stages shown in FIGS. FIG. 3 shows a first stage of mold opening, in which the fixed mold plate 2 is retreated integrally with the movable mold plate 1 and the space between the fixed mold plate 2 and the runner strip plate 9 is opened. At this time, since the tip of the reverse taper of the pin 9a provided on the runner strip plate 9 bites into the runner R, the runner R is held on the runner strip plate 9 side, and the cured resin is formed into a tapered cone with the disk gate 3. The runner R is separated from the runner strip plate 9 at the pinpoint connection portion of the resin supply path 2c. Further, the molded article G is held in the movable closed space. Also, the fixed mold plate 2 is controlled by a jig provided on the mold side surface so as not to retreat beyond this position.

Next, as shown in FIG. 4, the movable mold 1 is further retracted to separate the fixed mold 2 and the movable mold 1. Further, as a third stage of mold opening, the movable mold 1 is further retracted as shown in FIG.
Is relatively moved in the direction of the arrow, and the molded product G is ejected by the eject pins 7.

The ejecting operation is performed by restricting the eject plates 9 and 10 with a stopper (not shown) with respect to the moving mold that moves backward, and by moving the ejecting plates 9 and 10 relatively to the moving mold. At the time of this protruding operation, in the case of a helical gear or the like whose teeth are inclined with respect to the axis, since the outer case 1c is smoothly rotated by the bearing 1e, the tooth profile mold 1a is smoothly removed along the tooth trace. It will be typed. At the same time, the runner stripper plate 9 is moved to the movable mold plate 1 side by a jig provided on the mold side surface, and the runner R and the sprue S are separated from the runner stripper plate 9.

As shown in FIG. 6, the molded product G thus removed has a disk 3a on the inner diameter portion, but no gate mark on the outer surface of the product. Thereafter, the disk 3a remaining on the inner diameter of the molded product G is removed by opportunity processing to obtain a gear.

[0023]

EXAMPLE Next, a helical gear having the following characteristics was molded by a method of the present invention using polyamideimide (4203L, manufactured by Teijin Acomo Co., Ltd.) as a resin.

[Specification of helical gear] Gear specifications Standard tooth profile Normal tooth module M = 0.8 Pressure angle A = 20 ° Number of teeth Z = 20 Twist angle 20 ° Twist direction Right C. D φ17.027 O.D. D φ18.627 Number of mating teeth (3) 6.14

[0025] Tooth profile accuracy, tooth trace accuracy and JGMA
Table 1 shows the meshing accuracy. In Table 1, Comparative Example 1 was obtained by injection molding a helical gear having the same specifications with the same resin as above using a one-point pinpoint gate mold, and Comparative Example 2 was obtained by cutting and forming a helical gear having the same specifications. Is shown.

[0026]

[Table 1]

As is clear from Table 1, the embodiment of the present invention has a tooth profile, a tooth line and a JGMA in comparison with Comparative Example 1.
It was found that the meshing accuracy was good and that the molding could be performed with an accuracy comparable to that of the cutting molding.

[0028]

As described above, in the gear molding die of the present invention, since the disk gate is provided at the axial center of the shaft hole of the molded product, the resin which is radially spread and supplied by the disk gate is provided. The distance to the cavity end is small, and the filling is performed simultaneously in each direction.
Even when gears with a slender shape of 7 or more are molded with resin with poor fluidity, they can be filled sufficiently and no weld is generated.
It is possible to form a gear with good tooth profile transferability and high dimensional accuracy. Further, according to the gear manufacturing method of the present invention, in addition to the molding accuracy obtained by the mold, it is possible to obtain a gear with excellent surface properties without leaving gate traces on the side surface as well as the inner diameter surface as well as the gear surface. it can.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a gear molding die in a closed state.

FIG. 2 is an enlarged sectional view of a main part of a gear forming die.

FIG. 3 is a cross-sectional view of a gear molding die showing a first stage of demolding.

FIG. 4 is a cross-sectional view of a gear forming mold showing a second stage of demolding.

FIG. 5 is a cross-sectional view of a gear molding die showing a third stage of demolding.

FIG. 6 is a cross-sectional view of a molded product after demolding.

FIG. 7 is a sectional view of a conventional mold.

FIG. 8 is a cross-sectional view of another conventional mold.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Moving side mold plate 1a ... Gear tooth type mold 1b ... Moving side core pin 1c ... Outer insert 1d ... Inner insert 2 ... Fixed side mold plate 2b ... Fixed side core pin 2c ... Resin supply path 3 ... For disk gate 4 ... Receiving plate 5 ... Spacer 6 ... Moving side mounting plate 7 ... Eject pin 8a, 8b ... Eject plate 9 ... Runner strip plate 10 ... Locate ring 11 ... Fixed side mounting plate 12 ... Injection molding nozzle S ... Sprue R ... Runner G: Molded product

Claims (3)

[Claims] 1. A mold for injection molding a resin gear having a shaft hole through which a shaft is inserted and a tooth profile of an outer peripheral surface concentrically, wherein the gear tooth profile die 1a and a center of a moving side end face of the die 1a. A movable mold plate 1 having a core pin 1b protruding toward the fixed side, a core pin 2b facing the movable mold plate 1 and coaxial with the core pin 1b and protruding toward the movable mold, and penetrating through the core pin 2b. And a fixed side mold plate 2 having a resin supply passage 2c opening at the tip of the core pin 2b. When the mold is closed, the core pins 1b and 2b are coaxially aligned in the tooth form mold 1a and at the axial center. A gear forming die, wherein a gap 3 for a disc gate is formed between the tip surfaces of the opposed core pins 1b and 2b. 2. The tooth mold 1a of the movable side mold plate 1 is
c, and when the core pin 1b is fitted concentrically with the outer nest 1c, the inner nest 1d is formed, and the core pin 1b is rotatable about a gear shaft on which the outer nest 1c is formed. The gear molding die according to claim 1, wherein 3. The gear molding die according to claim 1 is closed, and the injected molten resin is formed on the front end facing surfaces of the core pins 1b and 2b via the sprue S, the runner R, and the resin supply path 2c. A gear forming step of filling the enclosed space from the disc gate 3 and cooling and solidifying; a separating step in which the runner is separated by the disc gate 3 and then a molded article G is protruded from a mold; and an inner periphery of the molded article G A gate removing step of removing the remaining disk 3a.