JPH0369697B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an injection molding die having an open core for molding a molded product having an undercut such as a helicoid screw on the inner peripheral surface.

[Prior Art] Conventionally, as an injection mold for molding a molded product having an undercut such as a helicoid screw on the inner peripheral surface, a helicoid screw is machined into the core of a movable mold, and this threaded core is used as an injection mold. The molded product can be released from the movable mold by rotating it through a rack and pinion mechanism that utilizes the opening of the mold.
As disclosed in Japanese Patent No. 25529, a configuration is adopted in which a threaded core is rotated by a motor and removed from the mold to be released from the mold.

By using such an injection mold, the threaded core is rotated to release the molded product, so the thread shape of the molded product is smooth, precise, and continuous. will be done. However, such injection molds have the problem that the mold structure becomes complicated, the molding cycle required to mold one molded product becomes longer, and the mold cost and molding cost increase. There are problems.

In order to solve such problems,
A technique disclosed in Publication No. 38032 has been proposed.
In the molding die disclosed in this publication, the core incorporated in the movable mold is divided into a central core that is not threaded and a pair of threaded split pieces, and the center core and split pieces are separated. are engaged in a dovetailed manner,
It is configured to move the split pieces along the axial direction by relative movement between the central core and the pair of split pieces, and to process undercuts such as helicoid screws that are partially formed on the inner peripheral surface. .

However, with this configuration, in the case of a molded product such as a camera lens barrel that has an undercut such as a helicoid screw over the entire inner circumference,
A helicoid screw must be machined into the center core, and in this case, the helicoid screw machined into the center core functions as an undercut, so there is a problem that the molded product cannot be released from the movable mold, that is, the screw core. In this way, if a continuous helicoid thread cannot be formed, it cannot be used as an injection mold for lens barrel molding, which requires helicoid threads in technical fields such as VTRs and cameras where automation is progressing. Become.

Japanese Patent Publication No. 59-14333 discloses a technique for molding a molded product such as a lens barrel having an undercut such as a continuous helicoid screw. According to the technique disclosed in this publication, a mold partial core a constituting an open core is connected to a conical central core b having an inclined surface having two types of inclination angles (α<β); It is divided into two types of split pieces c and d, which are machined with helicoid screws. Then, the splitting piece c is jointly engaged with the inclined surface of the central core at the inclination angle α, and one surface of the splitting piece c is used as the installation surface of the splitting piece d, and the splitting piece d is inclined at the inclination angle β of the central core b. It is configured for dovetail engagement with the surface. In this way, by the relative movement of the center core b and the split pieces c and d, both of the split pieces c and d are moved along the axial direction, thereby processing undercuts such as helicoid screws.

However, in a molding die having such a configuration, as shown in FIG. Therefore, one surface on both sides of the splitting piece c protrudes from the inclined surface having the inclination angle β of the central core b.

Here, since the split piece d is attached to the inclined surface of the center core b with an inclination angle β by a dovetail joint, the axial movement of the split piece d is prevented, and the molding of the movable mold is prevented. Release from the mold will not be achieved. Alternatively, if the split pieces c and d are forcibly moved along the axial direction, the split pieces d will be deflected radially outward from the inclined surface having the inclination angle β, and the dovetail engagement will be broken. That will happen.

In addition, as shown in FIG. 9, the center core b and each of the split pieces c and d are positioned through dovetail engagement as described above, so that they can Due to wear on the sliding surface (particularly the X portion shown in the figure), there is a risk that the dividing piece may shift as shown by the two-dot chain line. This shift in the position of the split piece causes steps and burrs to occur on the inner surface of the molded product, which poses a problem that reduces the yield of the molded product.

Therefore, in order to solve these problems,
A technique disclosed in Japanese Unexamined Patent Publication No. 150715/1988 is known.

In the mold member disclosed in JP-A No. 59-150715, the relative movement of the center core and the split piece along the axial direction allows the split piece to move along the axial direction while allowing movement in the radial direction. In order to make this possible, the dovetail engagement is achieved by a special dovetail shape, as shown in FIG.

[Problems to be Solved by the Invention] However, in the mold member disclosed in JP-A-59-150715, there is a special dovetail engagement between the center core b and the split pieces c and d. Since they are connected by , the split pieces c and d are set to be movable in the radial direction. Therefore, there is no problem in positioning the splitting pieces c and d if their radial dimensions are restricted by projections such as the slide core.
However, in other cases, the tips of the split pieces c and d are in a state of free movement along the radial direction. Therefore, at the timing of mold clamping, based on the difference in the frictional force between the splitting pieces c and d, and during the molding operation, based on the influence of the flow of molten resin in the cavity, the splitting pieces have a radius that is independent of each other. By sliding along the direction, a step is created between adjacent split pieces.

As a result of the occurrence of such a step, burrs and steps are generated on the inner surface of the molded product, which is a problem. In particular, there is a problem that this mold cannot be used for manufacturing camera lens barrels that require high precision such as dimensional tolerance of ±0.015 and concentricity of 0.03 or less. This invention was made in view of the above-mentioned problems, and an object of the invention is to accurately manufacture molded products having undercuts such as helicoid screws on the inner surface without burrs and without creating steps. It is an object of the present invention to provide an injection molding mold having an open core, which can realize accurate positioning of each split piece to a molding position.

[Means for Solving the Problems] In order to solve the above-mentioned problems and achieve the purpose, an injection molding mold having an open core according to the present invention has a central core that is gradually tapered;
Arranged to surround this central core,
It is equipped with a plurality of split pieces that define the inner peripheral surface of the cavity having an undercut, the center core and the split pieces are arranged on the movable mold or the fixed mold side, and each of the split pieces is attached to the center core. An injection molding mold having an open core is attached to the outer peripheral surface of the central core by a special dovetail engagement so as to be slidable along the central axis and in the radial direction. A first protrusion extending along the axial direction is provided on the distal end surface of the central core, and a second protrusion extending along the axial direction is provided on the distal end surface of each split piece,
In addition, a first recess into which the first protrusion is fitted and a second recess into which the second protrusion is fitted into a fixed mold or a movable mold on the side where the center core and the split piece are not arranged. The fitting between the first projection and the first recess defines the positioning of the fixed mold and the movable mold, and the fitting between the second projection and the second recess defines the positioning of the fixed mold and the movable mold. , the radial position of each split piece is defined.

[Function] In the injection mold configured as described above, each split piece is engaged with the center core by a special dovetail joint, so that the split pieces are attached to the outer circumferential surface of the center core along its central axis. Moreover, it is attached so as to be slidable along the radial direction. Then, at the molding position, the positioning of the fixed mold and the movable mold is defined by fitting the first protrusion of the center core into the first recess of the mold on one side, and the second projection of each split piece is fitted. The radial position of each split piece is defined by the fit between the projection and the second recess of the one side mold. In this way, even though each split piece is slidably attached to the central core along the radial direction, the molding position of each split piece is uniquely defined. .

[Example] The structure of an example of an injection molding mold having a listener core according to the present invention will be described below with reference to the first embodiment of the attached drawings.
This will be explained in detail with reference to FIGS. 8 to 8.

Although it is optional whether the center core and the split pieces are placed on the movable mold side or the fixed mold side, in this embodiment they are placed on the movable mold side.

As shown in FIG. 1, this injection mold includes a central core 12 constituting one component of a movable mold 10.
It is equipped with The central core 12 has side surfaces 14, 16 and 18, 20 that face each other at the same angle of inclination, and has a horizontal cross-sectional shape of a right-angled quadrilateral, whose cross-sectional area gradually decreases upward. It is formed into a truncated pyramid shape.

Each side surface 14, 16, 18 of this central core 12,
20 is the first to fourth split piece 22, 2 which will be described later.
4, 26, and 28 respectively. This central core 12 and four warikoma 22,
24, 26, and 28 constitute an open core. Further, special dovetail grooves 30 are formed in the center of the side surfaces 14 and 16 of the central core 12 so as to extend in the vertical direction, and in the center of the side surfaces 18 and 20 of the central core 12, special dovetail grooves 30 are formed so as to extend along the vertical direction. A dovetail groove 34 is formed to extend along the vertical direction.

On the other hand, a special dovetail 32 that engages with a corresponding special dovetail groove 30 protrudes from each side surface corresponding to each side surface 14, 16 of the central core 12 of each of the first and second split pieces 22, 24. It is formed. With these pair of special dovetail grooves 30 and special dovetail grooves 32,
It is configured to achieve a special dovetail engagement described below.

Furthermore, each of the third and fourth warikoma 26, 28
A dovetail 36 that engages with a corresponding dovetail groove 34 is formed protruding from each side surface corresponding to each side surface 18 and 20 of the central core 12 . These pair of dovetail grooves 34 and dovetails 36 are configured to achieve dovetail engagement, which will be described later.

The horizontal cross-sectional shapes of these first and second split pieces 22 and 24 define circular arcs that define outer peripheral surfaces 22a and 24a, and sliding surfaces 22b and 24b that come into sliding contact with corresponding side surfaces 14 and 16 of central core 12. It is set in a roughly half-moon shape surrounded by strings. Further, the horizontal cross-sectional shapes of the third and fourth split pieces 26 and 28 sandwiched between the first and second split pieces 22 and 24 are circular arcs that define the outer peripheral surfaces 26a and 28a,
A line segment defining sliding surfaces 26b and 28b that slide on the corresponding side surfaces 18 and 20 of the central core 12, and one guide surface that slides on the sliding surface 22b of the first split piece 22 adjacent on one side. 26c, 28c, and the other guide surface 26d that slides into sliding contact with the sliding surface 24b of the adjacent second splitting piece 24 on the other side,
It is set to have a modified rectangular shape that is surrounded by the line segment defining 28d and has a circular arc in part.

These first to fourth split pieces 22, 24, 26,
With the distal end surface of 28 set flush with the distal end surface of the center core 12, each split piece 22, 24, 26, 28
The outer circumferential surface of is configured to form a circumferential surface when these are combined. The outer circumferential surfaces of the combined splitting pieces 22, 24, 26, and 28 constitute the inner circumferential surface of the cavity that defines the molded product. A thread groove M defining a helicoid formed on the circumferential surface is continuously threaded.

As shown in FIG. 2, this thread groove M has a depth similar to that of the thread grooves in other parts near the joints of the split pieces 22, 24, 26, and 28 that are adjacent to each other. Sayori, it is set shallowly.
By making a difference in the depths of the thread grooves M and Ma in this way, the height of the thread blade of the helicoid screw in the molded product can be adjusted to 22, 24, 26,
It will be set low near the portion corresponding to the joint of No. 28. In this way, even if burrs occur on the threads of the joint,
Since this burr is small, it is prevented from protruding higher than the original top of the screw blade. Therefore, there is no possibility that this burr will impede the rotation of the molded product.

Further, FIG. 3 shows an enlarged view of the special dovetail shape of the above-described configuration. Here, since each special dovetail shape is the same shape in each of the first and second split pieces 22, 24, in the following explanation, one of them will be
This will be explained by using Warikoma 22 as a representative.

As shown in the figure, the special dovetail 32 is formed to protrude from the sliding surface 22b of the split piece 22 toward the center of the central core 12, and its horizontal cross-sectional shape is perpendicular to the sliding surface 22b. It is surrounded by a pair of upright proximal surfaces 32a, an inclined surface 32b protruding from the distal ends of these proximal surfaces 32a in an open state, a distal end surface 32c connecting the distal ends of these inclined surfaces 32b, and a protrusion 38 to be described later. is set to .
A protrusion 38 that further protrudes outward is provided on the distal end surface 32c of this special dovetail 32. This protrusion 38 is formed into a rectangular shape in horizontal cross section.

Here, both base end surfaces 32a and both side surfaces 38a of the protrusion 38 are both set parallel to each other from straight surfaces extending in the vertical direction.

On the other hand, the above-mentioned special dovetail groove 30 is formed so that the corresponding special dovetail 32 fits therein and guides the groove to slide along the vertical direction, while also allowing movement along the radial direction. There is. The horizontal cross-sectional shape of this special dovetail groove 30 is the same as the corresponding special dovetail groove 30.
A sliding surface 30a is disposed on the base end surface 32a of No. 2 so as to be slidable in the vertical direction and the radial direction, and a sliding surface 30a is disposed in parallel with a corresponding inclined surface 32b at an interval,
A contact surface 30b that can come into contact with this, and a sliding surface 22b of the central core 12 from the tip of each contact surface 30b.
It is set so as to be surrounded by an upright surface 30c that stands up perpendicularly to the bottom surface 30c, a bottom surface 30d that connects the tips of these upright surfaces 30c, and a groove 40 that will be described later. A groove 40 is formed on the bottom surface of the special dovetail groove 30, into which the protrusion 38 of the special dovetail 32 described above is slidably fitted.

Here, the sliding contact surfaces 30 that are in sliding contact with both base end surfaces 32a
a, and the side surface 4 that slides into contact with both side surfaces 38a of the protrusion 38.
0a are both set parallel to each other from straight surfaces extending in the vertical direction.

In addition, the third and fourth wari pieces 26, 28 mentioned above
The dovetail shape provided in is set to a shape similar to the special dovetail shape shown in FIG. Here, since each dovetail shape is the same in the third and fourth split pieces 26 and 28,
In the following explanation, one of them, the third split piece 26, will be explained as a representative.

That is, as shown in FIG. 4, this dovetail 36 is
It is formed in the same shape as the special dovetail 32 described above. Therefore, the reference numeral used in the explanation of the special case 32 will be changed to 36 in the drawing, and this explanation will be omitted. On the other hand, the dovetail grooves 34 are formed so that the corresponding dovetails 36 fit into them and are guided to closely slide in the vertical direction. The corresponding part has been removed. However, this standing surface 3
The configuration of the dovetail groove 34 except for not having 0c is the same as the special dovetail groove 30, so by changing the reference numeral used in the explanation of the special dovetail groove 30 to 34 and illustrating it, this dovetail groove 34 is shown. Description regarding the groove 34 will be omitted.

As shown in FIG. 5, this movable mold 10 includes a central core 12. still,
The configuration shown in FIG. 5 is V-V in FIG.
It is shown in an expanded state after being cut along the line. Here, the core plate 5 of the movable mold 10
2 is disposed in contact with the fixed mold on the mold release surface L0, and as described later, above the center core 12 in the figure is a fixed mold into which the tip of the central core 12 is fitted. A side cavity plate 54 is provided. Further, there is an inner peripheral surface between the inner peripheral surface of the core plate 52 and the outer peripheral surface of the tip portions of the first to fourth split pieces 22, 24, 26, and 28 disposed around the center core 12. A cavity 42 is defined in which a ring-shaped molded product with a thread groove is formed.

As described above, the inner surface of this cavity 42 has the first to fourth split pieces 22, 24, which function as components of the open core in the movable mold 10.
It is constituted by a tip portion on which thread grooves M 26 and 28 are threaded. Further, in the cavity plate 54 described above, a runner 56 is provided for introducing the molten resin constituting the molded product into the cavity 42.
A gate 58 is formed between the runner 56 and the cavity 42.

In this movable mold 10, the central core 12 is
It is fixed onto a movable side fixed base 44 via bolts 46. Further, a first support body 48 is placed on this fixed base 44 . This first support body 48 is connected to the third and fourth split pieces 26 and 28 described above.
It is configured so that these can be shifted in conjunction with the mold opening operation.

Furthermore, a second support 50 is disposed above the first support 48 . This second support body 50 is configured so that the first and second split pieces 22 and 24 can be shifted in conjunction with the mold opening operation.

Here, as described above, at the tip of the central core 12, there is a cylindrical positioning first protrusion 60.
is integrally formed and extends along its central axis. The outer circumferential surface of this first protrusion 60 is constituted by a straight circumferential surface parallel to the central axis. Further, a hole 62 into which the first protrusion 60 is inserted is formed in the cavity plate 54. Note that a tapered surface 60a is formed on the outer peripheral edge of the tip of the first protrusion 60 to facilitate fitting into the hole 62.

In addition, the first to fourth split pieces 22, 24, 26,
28 are integrally formed adjacent to each other, as shown in FIG. 5, and at the molding position that defines the cavity 42, they extend in the same direction as the first protrusion 60 described above in the united state. A second projection 64 is formed. That is, at the tips of each of the first to fourth split pieces 22, 24, 26, 28,
First to fourth protrusions 64a, 64b, 64c, 64d defining the second protrusion 64 in a combined state
are integrally formed. Note that these first to fourth protrusions 64a, 64b, 64c, and 64d are
All are shown in FIG. Here, as is clear from FIGS. 1 and 5, this second protrusion 64
is formed with an outer circumferential surface consisting of a tapered surface.

On the other hand, on the surface of the cavity plate 54 facing the second protrusion 64 formed in this way,
A fitting recess 66 is formed into which the second protrusion 64 is fitted in a complementary manner. In other words, the side surface of the recess 66 is formed into a tapered surface so as to come into contact with the tapered peripheral surface of the second protrusion 64 .

The operation of injection molding a molded product having an undercut using the injection mold configured as described above will be described in detail below.

The molten resin injected into the runner 56 via a spool (not shown) spreads through the gate 58 and fills every corner of the cavity 42 .
In addition, in this molding operation, that is, in the molding position, the protrusion portions 64 forming the second protrusions 64 formed on each split piece 22, 24, 26, 28, respectively.
The tip surfaces of a, 64b, 64c, and 64d are set flush with the tip surface of the central core 12, as shown in FIG. After this injection operation, after waiting for the molten resin to solidify, the movable mold 10 moves to the mold release surface L0.
It is separated from the fixed mold at the boundary. The molded product cooled and solidified within the cavity 42 is then released from the molding die by the method described below.

That is, since the thread grooves constituting the undercuts are formed on the inner circumferential surface of the molded product, the split pieces 22, 24, 26, 28 are simply removed from the molded product.
It is impossible to pull it out along the axial direction downward in the figure. Therefore, first, during the injection operation, the diameter of the outer periphery defined by these split pieces 22, 24, 26, and 28 is reduced so that it can be extracted from the molded product.

Therefore, as shown in FIG. 6, by first shifting the movable side fixed base 44 of the movable mold 10 downward in the figure by a predetermined amount, the first to fourth splitting pieces 22, 2
4, 26, 28 will be operated on the central core 12 as follows. That is, the first and second splitting pieces 22, 24 are movable relative to each side surface 14, 16 of the central core 12 along the axial direction by the special dovetail engagement, and are movable along the radial direction. The third and fourth splitting pieces 26, 28 are movably attached, while the third and fourth splitting pieces 26, 28 are connected by dovetail engagement.
It is attached in close contact with each side surface 18, 20 of the central core 12 so as to be relatively movable only along the axial direction.

Therefore, when the movable side fixed base 44 is shifted together with the center core 12, the corresponding side surface 18,
The central core 12 will be pulled down while sliding the center core 20 along it. Here, central core 1
2 is tapered upward, so depending on this lift, the third and fourth split pieces 2
6, 28, these sliding surfaces 26c, 26d; 28c, 28d are
Each will project radially outwardly from a corresponding side surface 14, 16 of central core 12. In other words, the sliding surfaces 26 of the third and fourth splitting pieces 26, 28
c, 26d; 28c, 28d are the corresponding sliding surfaces 22b, 28c, 28d of the first and second dividing pieces 22, 24, respectively;
24b will be biased radially inwardly.

In this way, first, the third and fourth warikoma 2
As shown in FIG. 6, the outer circumferential surfaces of 6 and 28 separate from the inner circumferential surface of the molded product, and the undercut comes off.

Here, regarding the first and second splitting pieces 22, 24, the outer circumferential surfaces of these splitting pieces 22, 24 are maintained in a state where they are engaged with the inner circumferential surface of the molded product. Therefore, in conjunction with the subsequent mold opening operation, the first support body 48 is then separated from the first support body 50, and the third and fourth split pieces 26, 28 are shifted downward together with the center core 12, The center core 12 is the first
and the second dividing piece 22, 24 only.

When the center core 12 slides the corresponding side surfaces 14 and 16 with respect to the first and second split pieces 22 and 24 in this way, the first and second split pieces 22 and 2
4 will be moved radially inward according to the inclination of these side surfaces 14, 16 to reduce their spacing. In this way, as shown in FIG. 8, the outer peripheral surfaces of the first and second split pieces 22, 24 are separated from the inner peripheral surface of the molded product, and the undercut is removed. That is, all warikoma 22, 24, 2
6 and 28 are separated inward from the inner peripheral surface of the molded product, and the molded product is set in a state where it can be freely extracted along the axial direction.

Finally, the mold release surface L0 is opened, and the molded product is taken out from the mold using a robot hand or the like as appropriate.

Here, in this embodiment, as described above, both the first and second split pieces 22 and 24 are
They are attached to corresponding sides 14, 16 of central core 12 by special dovetail engagements, respectively. In this special dovetail shape, as shown in FIG.
The side surface 40a of the groove portion 40 that is in sliding contact with the groove portion 40a is set to be a straight surface. Further, the base end surface 32a of the special dovetail 32 and the sliding contact surface 30a of the special dovetail groove 30 that slides thereon are as follows:
They are set to consist of straight surfaces.

By providing a straight surface in this way,
The first and second split pieces 22 and 24 are connected to the center core 12.
When the first and second splitting pieces 22, 24 are lifted while sliding on the corresponding side surfaces 14, 16 of
The movement along the axial direction is reliably guided by the sliding contact of these straight surfaces.

Next, a mold clamping operation for returning the molding die to its initial position after injection molding of a molded product having an undercut will be described.

As described above, after the molded product is released from the cavity 42, the mold clamping operation is started. That is, from the state shown in FIG. 8, the movable fixed base 44 and the first support 48 are raised so that the first support 48 comes into contact with the second support 50. In this way, first, the state shown in FIG. 6 is restored. Here, the first and second warikoma 22, 24 are
Due to the special dovetail engagement described above,
The first and second split pieces 22, 24 will slide relative to the central core 12, but their radial positions are such that no force is acting on them to bias them radially inward. Therefore, it remains located radially outward.

From this state shown in FIG. 6, the first and second supports 48, 50 rise together. In response to this integral rise, the first protrusion 60 of the central core first fits into the hole 62 of the cavity plate 54, and the center position of the central core 12 is accurately defined. In addition, in accordance with this integral rise, the first to fourth split pieces 22, 24, 26, and 28 are engaged in the above-mentioned dovetail joint, so that they are in relative sliding contact with the outer surface of the center core 12, and the radius It will move outward. At this time, since the radial positions of the first and second split pieces 22 and 24 are in the above-mentioned special dovetail engagement, they are somewhat unstable due to play.

Furthermore, the first and second supports 48, 5
0 rises together, so that the second protrusion 64 fits into the fitting recess 66. here,
Along with this fitting operation, the first and second protrusions 64a and 6 formed on the first and second split pieces 22 and 24, which constitute the second protrusion 64,
4b, these tapered circumferential surfaces engage with the slanted side surfaces of the recess 66, and are biased radially inward along the slanted surfaces of the recess 66.
In this way, the first and second projections 64a,
At the time when the tip end surface of 64b comes into contact with the bottom surface of the recess 66, the first and second splitting pieces 22, 24,
It is brought into a state of sliding contact with the outer surface of the central core 12.

In this way, the central core 12 and each split piece 2
2, 24, 26, and 28 are accurately returned to the molding positions shown in FIG.

As detailed above, according to this embodiment,
This means that unnecessary loads will not be applied to each other's straight surfaces. In this way, wear on the sliding surfaces of the special dovetail 32 and the special dovetail groove 30 is significantly reduced, and the split pieces 22, 24, 2
There is no possibility that the positions of 6 and 28 will be misaligned.
In this way, the position of the Warikoma does not shift, so
There are no steps or burrs on the inner surface of the molded product,
Therefore, the problem of poor yield of molded products does not occur, and molded products can be molded with high precision.

In addition, the first and second
Of course, the guidance of the dividing pieces 22 and 24 is effective not only for sliding along these axial directions, but also for moving along these radial directions.

Furthermore, such a structure having a straight surface is easy to manufacture, does not involve an excessive increase in manufacturing cost, and allows molded products to be manufactured economically and at low cost.

Furthermore, since the first and second split pieces 22 and 24 are attached to the center core 12 by the above-mentioned special dovetail engagement, these first and second split pieces 22 and 24 are attached in the radial direction. The amount of play will be set accordingly. Therefore, with the return operation to the molding position, these first and second split pieces 22, 2
In the position No. 4, there is a risk that the first and second split pieces 22 are left behind in the radial direction and cannot be accurately returned to the molding position. , 24, and the recess 66, the molding position is accurately positioned.

It goes without saying that this invention is not limited to the configuration of the one embodiment described above, and can be modified in various ways without departing from the gist of the invention.

For example, in the embodiment described above, the central core 12 is described as having a rectangular cross-section, but the central core 12 is not limited to such a configuration, and may be configured to have a hexagonal cross-section. good.

Furthermore, in the embodiment described above, the outer circumferential surface of the first protrusion 60 was described as being composed of a straight surface parallel to the central axis thereof, but the present invention is not limited to such a structure. For example, it may be configured to have a tapered shape and a tapered surface.

[Effects of the Invention] As described in detail above, the injection molding mold having an open core according to the present invention includes a gradually tapered central core, and is arranged so as to surround the central core, It is equipped with a plurality of split pieces that define the inner peripheral surface of the cavity having an undercut, the center core and the split pieces are arranged on the movable mold or the fixed mold side, and each of the split pieces is attached to the center core. An injection molding mold having an open core is attached to the outer peripheral surface of the central core by a special dovetail engagement so as to be slidable along the central axis and in the radial direction. A first protrusion extending along the axial direction is provided on the distal end surface of the central core, and a second protrusion extending along the axial direction is provided on the distal end surface of each split piece, and A first recess into which the first protrusion is fitted, and a second recess into which the second protrusion is fitted, in a fixed mold or a movable mold on the side where the center core and split piece are not arranged. The first
The fitting between the projection and the first recess defines the positioning of the fixed mold and the movable mold, and the fitting between the second projection and the second recess defines the radial position of each split piece. It is characterized by being

Therefore, according to the present invention, a molded product having an undercut such as a helicoid screw on the inner surface can be manufactured with high precision and at low cost, and it is also possible to accurately position each split piece at the molding position. An injection mold with an open core that can be used will be provided.

[Brief explanation of drawings]

Fig. 1 is an exploded perspective view showing the structure of an open core, which is a main part of an embodiment of an injection mold according to the present invention; Fig. 2 is a top view showing the top shape of the open core before injection operation. ; Figure 3 is a horizontal sectional view showing the configuration of a special dovetail shape; Figure 4 is a horizontal sectional view showing the configuration of a special dovetail shape; Figure 5 is a horizontal sectional view showing the configuration of a movable mold with an open core; In the figure, V-V
A side sectional view showing the movable mold in an injection operation state after being cut along a line and expanded; FIG. 6 is a side sectional view showing the movable mold with the movable side fixed base shifted; FIG. FIG. 6 is a top view showing the upper surface shape of the open core in the state shown in FIG. 6; FIG. 8 is a side sectional view showing the movable mold with the first support body shifted; FIG. A top view for pointing out the problems of Japanese Patent Publication No. 59-14333; and FIG. 10 is a top view for pointing out the problems of Japanese Patent Application Laid-open No. 59-150715 as a prior art. In the figure, 10...movable mold, 12... center core,
14; 16; 18; 20...side, 22; 24;
26; 28... Warikoma, 22a; 24a; 26a;
28a...Outer peripheral surface, 22b; 24b; 26b; 2
8b...sliding surface, 26c; 28c...one guide surface, 26d; 28d...other guide surface, 30
...Special groove, 32...Special groove, 34...Dove groove, 36...Present, 30a; 34a...Sliding surface, 30b; 34b...Abutting surface, 30c...Rising surface, 30d; 34d ...Bottom surface, 32a; 36a...
... Proximal end surface, 32b; 36b... Inclined surface, 32c;
36c...Tip surface, 38...Protrusion, 38a...Side surface, 40...Groove, 40a...Side surface, 42...Cavity, 44...Movable side fixing base, 46...Bolt, 48...First support body, 50... second support body, 52... core plate, 54... cavity plate, 56... runner, 58... gate, 6
0...first protrusion, 60a...tapered surface, 62...
...hole, 64... second protrusion, 64a; 64b;
64c; 64d... protrusion, 66... fitting recess.

Claims (1)

[Claims] 1. A central core that is gradually tapered, and a plurality of split pieces that are arranged to surround the central core and define the inner circumferential surface of a cavity that has an undercut. However, the center core and the split pieces are arranged on the movable mold or the fixed mold side, and each split piece has a special dovetail engagement with the center core, so that the split pieces are attached to the outer peripheral surface of the center core.
In an injection molding mold having an open core, the injection mold is slidably attached along the central axis and along the radial direction, and the injection molding mold has an open core that extends along the axial direction on the distal end surface of the central core. A first protrusion is provided on the tip surface of each split piece,
A second protrusion extending along the axial direction is provided, and the first protrusion is fitted into a fixed mold or a movable mold on the side where the center core and the split piece are not arranged. A first recess and a second recess into which the second protrusion is fitted are provided, and the fitting of the first protrusion and the first recess defines the positioning of the fixed mold and the movable mold. An injection molding mold having an open core, characterized in that the radial position of each split piece is defined by fitting between the second protrusion and the second recess. 2. The first protrusion has an outer circumferential surface parallel to the central axis of the central core, and the first recess has an inner circumferential surface that slides in sliding contact with the outer circumferential surface of the first protrusion in the axial direction. An injection molding mold having an open core according to claim 1. 3. Each of the second protrusions has an arcuate outer periphery concentric with the central core, and has a tapered outer peripheral surface inclined with respect to the central axis of the central core.
3. The injection molding mold having an open core according to claim 2, wherein the recess has an inner circumferential surface that abuts along the outer circumferential surface of the second protrusion. 4. Claim 3, wherein a tapered portion is formed on the tip edge of the first protrusion to facilitate fitting of the first protrusion into the first recess. An injection mold having an open core as described in . 5. The injection molding mold having an open core according to claim 4, wherein the first protrusion is located forward in the closing direction from the front end surface of the second protrusion. 6. The special dovetail and special dovetail groove that constitute the special dovetail engagement are characterized in that they have straight surfaces that slide into contact with each other and are parallel to a plane that includes the central axis of the special dovetail joint and the central core. An injection mold having an open core according to claim 1. 7. Each of the above-mentioned special dovetails is formed on the outer circumferential surface of the split piece on the central core side, and has a pair of proximal surfaces standing perpendicular to the outer circumferential surface, and an inclined surface protruding outward from the tips of these proximal surfaces in an open state. and a tip surface that connects the tips of these sloped surfaces, and the tip surface of this special dovetail is provided with a protrusion that projects outward, and each of the special dovetail grooves is connected to the corresponding special dovetail groove. A sliding surface disposed on the proximal end surface so as to be slidable in the vertical direction and the radial direction, a contact surface disposed parallel to the corresponding inclined surface and capable of abutting thereon, and each contact surface. The special dovetail groove has an upright surface that stands up perpendicularly to the outer circumferential surface of the central core from the tip of the contact surface, and a bottom surface that connects the tips of these upright surfaces, and the special dovetail protrusion is fitted into the bottom surface of this special dovetail groove. A groove portion is formed to fit together, and the straight surface is defined on both side surfaces of the special dovetail protrusion, and the straight surface is defined on both side surfaces of the groove portion of the special dovetail groove with which these side surfaces slide. An injection mold having an open core according to claim 6. 8. Claim 7, wherein the straight surface is defined on the base end surface of the special dovetail, and further defined on the sliding contact surface of the special dovetail groove with which these base end surfaces slide. An injection mold having an open core as described in .