JPH0557760A - Injection mold having undercut part - Google Patents

Abstract

PURPOSE:To provide the above mold capable of ensuring cavity accuracy preventing the abrasion of a dovetail engaging part because the accurate positioning between a center core and a slide roller can be performed and capable of being constituted relatively simply. CONSTITUTION:A pair of first open cores 5 each having the slide surface 8 sliding and moving along the side surface 2 having a small angle of inclination of a center core 1 and the mating surface 6 vertical to a large circular arc screw part 5a formed thereto and a pair of second open cores 9 each having the slide surface sliding and moving along the side surface 3 having a large angle of inclination of the center core 1 and the mating surface 10 vertical to a small circular arc screw part 9a formed thereto are provided and, by moving the center core 1 at the time of mold opening, the second open core 9 is moved faster than the first open core 5 and the mating surfaces 6, 10 are made movable parallel.

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 having an undercut portion, and for example, an undercut portion suitably applied for injection molding a molded product having an inner peripheral thread portion in the undercut portion. And an injection mold having

[0002]

2. Description of the Related Art Conventionally, there has been known a technique of using an injection molding die having an open core or a slide core for injection molding a molded product having an undercut portion. Japanese Examined Patent Publication No. 59-14333 is an example of such an injection molding die, and according to the present proposal, it is configured by providing two groups of six slide pieces engaged by dovetail grooves on the outer peripheral surface of the central core. By moving the central core in the mold opening direction when the mold is opened, each slide piece engaged in the dovetail groove can be moved inward in the diametrical direction to take out the molded product after molding. It is something to do.

Further, according to Japanese Patent Application Laid-Open No. 59-150715, it is proposed that a pair of dovetail groove engaging portions provided in the injection molding die have a special shape to prevent interference between the slide pieces. Has been done. On the other hand, JP-A-61-748
According to the "Undercut molding method" of Japanese Patent No. 17, there is proposed a structure in which large and small slide pieces are moved by an angular pin provided on a movable side mold plate.

FIG. 8 is a diagram for explaining the operation disclosed in Japanese Patent Laid-Open No. 61-74817. This figure shows that after forming a molded product H, the mold is opened and
It is shown that the slide piece is moved to the inner diameter side of the undercut portion. In the figure, the center pin 31 is provided through the through hole formed at the center of the taper pin 32 whose lower end is fixed to the ejector plate and whose outer peripheral surface is tapered. Further, the angular pins 18 are radially fixed in the circumferential direction of the taper pin 32 whose lower end is fixed to the movable mold plate 19, and the working ends are holes 50a and 90a provided in the large and small slide pieces 50 and 90.
The large slide piece 50 having a larger arc-shaped undercut portion has a hole 50a formed in an elongated hole shape, while the small slide piece 90 formed with a small arc-shaped undercut portion. The hole 90a is formed in a substantially circular shape.

In the "undercut molding method" of Japanese Patent Laid-Open No. 61-74817 described above, when the mold is closed, the slide pieces 50 and 90 radially arranged are closely attached to the taper surface of the taper pin 32. By doing so, an undercut portion for forming the molded product H is formed by opening in the outer diameter direction to form the undercut portion. Thereafter, as shown in the above figure, first, the small slide piece 90 having a small arc-shaped undercut portion is moved in the inner diameter direction by the mutual movement action of the hole 90a and the angular pin 18, and the large slide piece 50 is moved. After securing the space for moving, the hole 50a of the large slide piece 50 and the angular pin 18 move in the inner diameter direction by the mutual movement action.

[0006]

However, according to the proposal of Japanese Patent Publication No. 59-14333, one surface of a pair of slide pieces engaged with a central core in a dovetail groove is used as a slide surface of another slide piece. As a result, the divided surface of the slide piece is always a sliding surface, and wear of the slide piece occurs. Further, since the central core and the slide piece are positioned by the dovetail groove engaging portion, there is a problem that if the dovetail groove engaging portion wears, the central core and the slide piece cannot be accurately positioned.

On the other hand, in the proposal of Japanese Patent Laid-Open No. 59-150715, when the slide piece moves in the diametrical direction when the mold is opened, the special dovetail groove engaging portion is abraded, so that the central core is eventually brought about. There is a problem that accurate positioning between the slide piece and the slide piece cannot be performed. In addition, JP-A-61-7
In Japanese Patent No. 4817, a center pin is provided in a penetrating state with respect to a taper pin and a large number of slide pieces are radially arranged, which causes a problem that a die is complicated. Further, since the structure depends on the mutual movement action of the hole of each slide piece and the angular pin in order to move each slide piece to the inner diameter side, a guide portion for moving each slide piece to the inner diameter side is required. However, there is a problem that the mold becomes more complicated.

Further, there is a problem that burrs are generated at the portion of the molded product formed at the joint of the slide pieces. Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to ensure accurate positioning between the central core and the slide piece, thereby ensuring accuracy and preventing wear of the dovetail groove engaging portion. An object of the present invention is to provide an injection molding die having an undercut portion that can be formed and that can be configured relatively easily.

[0009]

[Means for Solving the Problems] and

In order to solve the above-mentioned problems and to achieve the object, an injection molding die having an undercut portion of the present invention has a central core gradually tapered and a center line in the longitudinal direction of the central core. An injection molding apparatus having a plurality of open cores, each of which has an undercut portion whose outer dimension changes along with the movement thereof, and which is arranged in a cavity so as to surround the periphery of the central core. High accuracy of the cavity at the time of mold closing is ensured by forming the mating surface with a plane parallel to the center line and by arranging the open core to follow the movement of the center core. And works to improve durability.

Further, preferably, in order to form the undercut portion in an inner peripheral thread shape, the central core is formed in a substantially quadrangular truncated pyramid shape in which opposing side surfaces are formed with a small inclination angle and a large inclination angle. A pair of first open cores forming a sliding surface, a large arcuate screw portion, and the mating surface that slide along the side surface of the small inclination angle, and slide along the side surface of the large inclination angle It comprises a pair of second open cores having a moving slide surface, a small arcuate screw portion and the mating surface, and the second open core side is moved earlier than the first open core by the movement. It is configured to move, and it works to secure the high accuracy of the cavity in which the undercut portion has an inner peripheral screw shape when the mold is closed and to improve the durability.

Further, preferably, the slide surface slidingly moving along the side surface of the small inclination angle and the slide surface slidingly moving along the side surface of the large inclination angle are engaged with the dovetail groove to add the additional surface. It is configured to move so as to ensure high accuracy of the cavity and improve durability. Further, it is preferable that a molding recess is formed at the seam toward the central core so that burr after molding does not occur in screwing. That is, the screw shape at the joint is
The first open core and the second open core are formed so as to be shallower than the screw shapes formed so that burr formation after molding does not affect screwing.

Further, preferably, a flange having the open core that slides and moves with respect to a guide portion formed along the side surface of the central core, and a hole formed integrally with the open core. And the angular pin that is inserted into the hole are provided in the movable mold, and the dovetail groove is not required, so that the injection mold having the undercut portion can be easily configured. Further, preferably, in order to provide four or more open cores, the central core is formed of a polygonal pyramid,
Further, it is possible to form a cavity having a complicated undercut portion.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a three-dimensional exploded perspective view of an injection-molding die having an undercut portion according to a first embodiment, showing only a main part configuration and at a molding position shown by a two-dot chain line in the figure. Although the slide pieces 5 and 9 are assembled in a state where the undercut portions of the slide pieces 5 and 9 are located, the slide pieces 5 and 9 are shown separated from the central core 1 for the sake of explanation.

In the figure, as shown in the figure, the central core 1 is formed in a truncated pyramid shape whose side surface gradually decreases from the mounting portion 1b to the movable die toward the upper surface 1a, while facing each other. And the first inclined surface 2 having an inclination angle θ1 formed by the plane Q perpendicular to the central axis of the central core 1 in the longitudinal direction, and the first inclined surface 2 are also formed to face each other, and the center of the central core 1 in the longitudinal direction is formed. It has a second inclined surface 3 having an inclination angle of θ2 with the plane Q perpendicular to the axis.

These inclination angles θ1 are, for example, 4 degrees, θ1
By setting the angle to 8 degrees, it is possible to make a difference in the movement amount of each slide piece described later. Further, the first inclined surface 2 has slide guide surfaces 2a parallel to each other on its side surface,
The large slide piece 5 is configured to be slidably guided on the slide side surface 8a. Further, by fitting into the convex groove portions 7 formed on the large slide piece 5 and the small slide piece 9, respectively, at substantially the centers of the first and second inclined surfaces 2 and 3 described above,
Dovetail grooves 4 which can be slid after assembly but cannot be separated from the angled inclined surfaces 2 and 3 are machined as shown by opening upper and lower ends respectively.

As shown in the figure, the second inclined surface 3 has a side surface gradually narrowing from the upper surface portion 1a to the mounting portion 1b, and is formed by a plane intersecting with the slide guide surface 2a. Next, as shown in the figure, the large slide pieces 5 assembled in a pair so as to face each other include a slide surface 8 that slides along the first inclined surface 2 having the above-described inclination angle θ1, and a center of the slide surface 8. The convex groove portion 7, the large arcuate screw portion 5a forming a part of the above-mentioned undercut portion, and the mating surface 6 formed by a plane parallel to the central axis of the central core 1 in the longitudinal direction are formed symmetrically. ing.

Further, as shown in the figure, the construction of the small slide pieces 9 assembled in a pair so as to face each other is as follows.
Slide surface 11 slidingly moving along the second inclined surface 3
A central convex groove portion 7 of the slide surface 11, a small arcuate screw portion 9a forming a part of the undercut portion, and a flat surface parallel to the central axis of the central core 1 in the longitudinal direction. The surface 10 is formed symmetrically while the flank 12
Is formed.

The convex groove portion 7 is formed in the dovetail groove 4 of the central core 1 described above.
Is inserted from the opening and assembled, so that the pair of small arc-shaped screw parts 9a and the pair of large arc-shaped screw parts 5a are located at the molding position 20 shown by the chain double-dashed line. Perform molding. Forming position 2 shown by the two-dot chain line
In order to make it zero, the slide surface 8 of the large slide piece 5 moves while being slid with respect to the first inclined surface 2, while the slide surface 11 of the small slide piece 9 moves to the second inclined surface 3.
It moves while sliding with respect to, but before and after this, the mating surfaces 6, 10 are moved in parallel so that they come close to each other, and finally they come into close contact with each other to reach the molding position 20 shown by the chain double-dashed line.

FIG. 2 shows how the mold is opened after the above molding.
The operation will be described with reference to the operation explanatory diagram. When the mold is opened after molding, the central core 1 is moved in the direction of arrow A in the figure, but the large slide piece 5 and the small slide piece 9 are prevented from moving in the direction of arrow A by a mold plate (not shown). Since it is restricted, it starts to move inward in the diameter of the molding position 20. That is, a component force of moving in the direction of arrow A acts on the large slide piece 5 engaged with the dovetail groove 4 of the first inclined surface 2,
Heading to the center in the direction of arrow C in the figure. The central core is A
The central core upper surface is lower than the surface positions of the upper surface 5b and the upper surface 9b of the slide piece during operation.

Further, the component force moving in the direction of arrow A also acts on the small slide piece 9 engaged with the dovetail groove 4 of the second inclined surface 3 to move it to the center in the direction of arrow B in the figure. As described above, the inclination angle θ1 of the first inclined surface 2 is set to 4 degrees, while the inclination angle θ2 of the second inclined surface is doubled to 8 degrees, as described above. Since the amount of movement in the direction of arrow B is twice the amount of movement of the large slide piece 5 in the direction of arrow C, the small slide piece 9 moves to the center side earlier than the large slide piece 5, thus reducing the diameter. You can move in any direction. Further, the interference between the slide pieces 5 and 9 when the mold is opened is prevented.

On the other hand, when the central core 1 is moved in the direction opposite to the arrow A and the slide cores 5 and 9 are moved in the direction opposite to the arrows B and C, the mold is closed again for the preparation for molding and the slide cores 5 and 9 are moved upward. Although it is moved and moved to the position shown by the two-dot chain line in the figure, the joints 6 and 10 of the slide pieces 5 and 9 are moved in parallel as described above to be in close contact with each other. No wear on the eyes 6, 10 will occur. Further, since the large slide piece 5 is also slidably guided by the side surface 8a of the slide surface 8, the movement in the arrow direction C can be smoothly performed.

Next, FIG. 3 is a front view of the injection molding die according to the second embodiment, in which the slide pieces 5 and 9 are placed under the molding position 20 shown by the chain double-dashed line in FIG. It shows how the cut part is located. In this figure, since the basic configuration has been described with reference to FIGS. 1 and 2, the details are given the same reference numerals, and the description will be omitted and only the different parts will be described.
The upper surface portion 1a of the central core 1 and the upper surface portions 5b, 9b of the slide pieces 5, 9 are flush with each other, and the seam 6,
10 has been moved to be in close contact. In this state, the undercut portion having the outer dimension D is formed by the pair of small arc-shaped screw portions 9a and the large arc-shaped screw portion 5a, and the convex mating portions 14 having the width dimension w and the height dimension h are fitted together. Formed in eyes 6 and 10.

With the above construction, when a gap is formed in the joints 6 and 10 after the mold has been used for a long period of time, a burr generated by entering the gap is generated on the molded product side. By the above-mentioned convex mating portion 14,
Since a burr is formed on the inner diameter side of the screw part of the molded product, the effect of the burr does not affect the function of the screw part. Therefore, if the above-mentioned height dimension h is set to 0.1 mm, the effect of the burr does not affect the function of the screw portion if the burr height is 0.1 mm or less. By the way, when the height dimension h is set to 0.1 mm, the D dimension is 5
Good results could be obtained by setting the width to 7 mm and the w dimension to 4 mm.

Next, FIG. 4 is a front view of the injection molding die according to the third embodiment, and FIG. 5 is a sectional view of the main part of the injection molding die, showing the mold closed state. First, FIG. 4 shows a state in which the undercut portions of the slide pieces 5 and 9 are located at the molding position 20 shown by the chain double-dashed line in FIG. In this figure, the basic structure has already been described with reference to FIGS. 1 and 2, and the details will be given the same reference numerals and the description will be omitted and the description will be limited to different parts. The upper surface of the central core 1 and the slide piece 5, Each upper surface of 9 is flush with each other, and the joints 6 and 10 are moved so as to be in close contact with each other. In this state, the undercut portion is formed by the pair of small arc-shaped screw parts and large arc-shaped screw parts.

Further, the dovetail grooves 4 formed on the respective inclined surfaces of the central core 1 have vertical side surfaces on both sides as shown in the drawing, and convex dovetails directly inserted into the dovetail grooves 4 are formed. Slide pieces 5 and 9 each provided with a groove portion 7 are provided so as to be movable on four side surfaces as shown in the drawing. Flange portions 5f and 9f extending radially from the central core 1 are integrally formed on the slide pieces 5 and 9, and holes 5g and 9g formed in the flange portions 5f and 9f will be described later. The angular pins 18 are put into the respective inserted states.

Next, in FIG. 5, a fixed side mold 16 is formed with a runner for injection of resin, a gate and a hole 16a, and in the mold closed state shown in the figure, a cavity formed by the above-mentioned undercut portion. While allowing molten resin to be injected therein, the mutual positional relationship between the fixed side mold 16 and the central core 1 is determined by inserting the bolt 15 that is screwed into the threaded portion of the central core 1 into the hole 16a. I am able to do it.

The fixed mold 16 is provided with a movable mold plate 17 having the first separation surface P1 as a separation surface and a receiving plate 19 having the second separation surface P2 as a separation surface with respect to the movable side mold plate 17. The molds are provided so as to be movable so as to be in a mold closed state and a mold opened state, respectively, to form a known mold structure. Further, the sliding guide plate 21 having the elongated hole 21b for allowing the angular pin 18 to be inserted is provided with the spacer 22 by using the bolt 15.
Is fixed to the movable-side mold plate 17 via a sliding surface 21a of the sliding guide plate 21 and the sliding surface 17a of the movable-side mold plate 17 to form a space portion. The flange portions 5f and 9f of 5 and 9 are slidable within this space portion.

On the other hand, a female part 17a is formed on the movable side mold plate 17, and a cavity is formed by a pair of small arc-shaped screw parts 9a and large arc-shaped screw parts 5a which are the undercut parts of the slide piece. ing. Further, as described above, the central core 1 fixed to the receiving plate 19 by the bolts 15 and moved in the direction of arrow A in the figure has the side surface gradually becoming smaller from the mounting portion 1b for the movable die toward the upper surface 1a. The first inclined surface 2 is formed in the shape of a quadrangular pyramid, and is formed to face each other, and the inclination angle formed by the plane Q perpendicular to the central axis of the central core 1 in the longitudinal direction is θ1.
And a second inclined surface 3 which is also formed to face each other and which has an inclination angle of θ2 with the plane Q perpendicular to the central axis of the central core 1 in the longitudinal direction.

These inclination angles θ1 are, for example, 4 degrees, θ1
By setting 8 degrees, the amount of movement of the large and small slide pieces 5 and 9 is made different. Further, the angular pin 18 fixed to the receiving plate 15 with the bolt 15 is used.
When the mold is closed, the tip thereof sneaks into the negative hole portion 17c of the movable mold plate 17, and the slide pieces 5, 9
Of the flanges 5f and 9f of the respective holes 5g and 9g, which are slanted at inclination angles θ1 and θ2, respectively, and are slidably received in the holes 5g and 9g. It is tilted and fixed to the plate 19.

In the above structure, when the resin is injected into the cavity and curing is waited for, and the molds are opened on the separation surfaces P1 and P2, the central core 1 is moved in the direction of arrow A in the figure, The slide piece 5 and the small slide piece 9 are restricted so as not to move in the arrow A direction as described above, and as described with reference to FIG. Start moving. That is, due to the holes 5g and 9g which sneak into the angular pin 18 without play, a component force moving in the direction of arrow C acts on the large slide piece 5 and moves toward the center.

An arrow A also appears on the small slide piece 9 (not shown).
The component force moving in the same direction acts toward the center of the central core in the same manner, but as described above, the inclination angle θ1 of the large slide piece 5 is set to 4 degrees while the inclination angle of the small slide piece 9 is set. Since θ2 is doubled to 8 degrees, the amount of movement of the small slide piece 9 in the direction of arrow B is twice the amount of movement of the large slide piece 5 in the direction of arrow C, so the small slide piece 9 is larger. Since it moves to the center side earlier than 5, each piece can be moved in the direction of reducing the diameter. Further, the interference between the slide pieces 5 and 9 when the mold is opened is prevented.

On the other hand, when the central core 1 is moved in the direction opposite to the arrow A and the slide cores 5 and 9 are moved in the direction opposite to the arrows B and C, the slide pieces 5 and 9 are moved upward while the mold is closed again for preparation for molding. Although the slide pieces 5 and 9 are moved to the positions shown in the drawing to be in a molding preparation state, the joints 6 and 10 of the slide pieces 5 and 9 are moved in parallel as described above to be in close contact with each other. No wear of 6, 10 will occur. Further, since the dovetail groove engaging structure may be processed into the extremely simple groove shape in which the undercut portion is not formed on the side surface as described above, the manufacture of the central core 1 and each slide piece 5, 9 becomes easy, Processing costs are greatly reduced.

Next, FIG. 6 is a front view of an injection molding die according to the fourth embodiment. In this figure, the basic configuration is shown in FIGS.
Since it has already been described, the details will be denoted by the same reference numerals and the description will be omitted to limit the description to the different parts. In place of the dovetail groove of the central core 1, a convex guide is provided on each inclined surface of the central core 1. Part 40
Are integrally formed in a cross shape. In addition, the large and small slide pieces 5 and 9 are formed with guide recesses 70 that are slidable by entering the guide portions 40. According to the central core described above, the mold can be further simplified.

Finally, FIG. 7 is a front view of the central core according to the fifth embodiment, in which the central core 1 is formed by a hexagonal pyramid as shown in order to provide four or more slide pieces. , A total of 6 slide pieces can be moved radially of the central core. As described above, according to each embodiment, the positioning accuracy between the central core 1 and each slide piece 5, 9 can be realized by the mating surfaces 6, 10, so that the cavity accuracy can be ensured and the dovetail groove engaging portion can be secured. Wear can be prevented. Further, by using the Eingular pin, it is possible to provide an injection molding die having an undercut portion that can be more easily configured. In addition, in each of the above-described embodiments, only the case where the undercut portion is formed as a helicoid screw formed in the lens barrel has been described, but the present invention is not limited to this, and a precision component having an undercut portion is used. Anything is fine.

[0035]

As described above, according to the present invention, since accurate positioning can be performed between the central core and the slide piece, accuracy can be ensured, wear of the dovetail groove engaging portion can be prevented, and relatively easily. It is possible to provide an injection molding die having a configurable undercut portion.

[Brief description of drawings]

FIG. 1 is a first injection molding die having an undercut portion.
It is a three-dimensional disassembled perspective view which concerns on an Example.

FIG. 2 is an external perspective view for explaining the operation of FIG.

FIG. 3 is a front view of an injection molding die having an undercut portion according to a second embodiment.

FIG. 4 is a front view of an injection molding die having an undercut portion according to a third embodiment.

5 is a fragmentary cutaway view of an injection mold using the central core and the slide piece of FIG. 4. FIG.

FIG. 6 is a front view of an injection molding die having an undercut portion according to a fourth embodiment.

FIG. 7 is a front view of a central core according to a fifth example.

FIG. 8 is a fragmentary cutaway view of a conventional injection molding die having an undercut portion.

[Explanation of symbols]

 1 central core, 2 first inclined surface 3 second inclined surface 4 dovetail groove 5 large slide piece 6 mating surface 7 convex groove 8 slide surface 9 small slide piece 10 mating surface 11 slide surface 12 angular surface 18 angular pin 20 at the molding position is there.

Claims (6)

[Claims] 1. A center core that is gradually tapered, and an undercut portion whose outer dimensions change as the center core moves along a center line in the longitudinal direction,
In an injection-molding die having a plurality of open cores arranged in a cavity so as to surround the center core, a mating surface between the open cores is formed as a plane parallel to the center line, and An injection molding mold having an undercut portion, characterized in that the open core is configured to follow the movement of the central core. 2. The center core, which is formed into a substantially quadrangular truncated pyramid shape, in which opposite side surfaces are formed with a small inclination angle and a large inclination angle in order to form the undercut portion in an inner peripheral thread shape, and the small core. A pair of first open cores having a sliding surface slidably moving along the side surface of the slant angle, a large arcuate screw portion, and the mating surface, and a slide slidingly moving along the side surface of the large slant angle. A pair of second open cores each having a surface, a small arcuate threaded portion, and the mating surface, and moving the second open core side faster than the first open core by the movement. The injection-molding die having an undercut portion according to claim 1, which is configured as described above. 3. The dovetail groove engagement between a slide surface slidingly moving along the side surface of the small inclination angle and a slide surface slidingly moving along the side surface of the large inclination angle to perform the pursuit. It is constituted as follows, Claim 1 or Claim 2 characterized by the above-mentioned.
An injection-molding die having an undercut portion as described in 1. 4. The injection-molding die having an undercut portion according to claim 1, wherein a molding recess toward the center core is formed at the seam. 5. The open core that slidably moves with respect to a guide portion formed along the side surface of the central core,
5. A flange portion having a hole formed integrally with the open core and an angular pin inserted into the hole are provided in a movable mold. An injection-molding die having an undercut portion as described in 1. 6. The injection molding having an undercut portion according to claim 1, wherein the central core is formed of a polygonal pyramid in order to provide four or more open cores. Mold.