JP3421948B2 - Injection molding method for bowl-shaped articles having undercuts - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] The present invention relates to an undercut portion.
For molding resin bowl-shaped articles having
The present invention relates to a manufacturing method. [0002] Injection molding is used for molding thermoplastic resins.
It is widely known as a typical example. This fire
In the injection molding method, if the resin material is put into the hopper,
Automatic molding and efficient mass production of products
There is a feature that can be. Also, injection molding method
The so-called injection molding machine is used for the
It can be roughly divided into two types in terms of structure. First of all
Is what is called a plunger type.
Can be moved forward and backward in a piston type
There is a mechanism, the resin is pushed forward by the plunger
Is what is done. Where the resin is a heated cylinder
Is melted through the gap between
This plunger is extruded into a mold.
Ip is often found in small injection molding machines. Next,
The other type is a screw type. This
Here, the screw is moving as the resin advances through the groove
The resin melts and recedes, and the molten resin accumulates in the heating cylinder
Swelling, and when enough is accumulated for one shot,
The screw advances and the molten resin is extruded into the mold.
This screw type thing is resin and
Good kneading of pigment, high injection pressure, high plasticizing ability
It is widely used. On the other hand, a mold used in the above injection molding method is
This is called an injection mold. This injection molding mold is
It is the heart of die forming, and the design of the mold is good or bad.
It is said that the quality of goods is affected. For example, molding
The protrusion of the resin to the end of the product is called burrs.
Due to poor adhesion of the parting surface of the mold
You. In addition, so-called sink, which is a depression on the surface of the molded product,
Warpage, bending, twisting, and joining of injected resin
Weld lines that create streak patterns with seams
Scratches, cracks, cracks, whitening, burnt, black on feet and molded products
It is pointed out that due to improper design of the mold,
Has been plucked. Here, the basic structure of a general injection molding die
The structure consists of a fixed mold and a movable mold.
Cores and cavities designed in a predetermined shape between the mating surfaces
Flow that guides the prescribed molten resin into the space formed by the
Roads are provided. Here, molten resin is generally injected
From the molding machine nozzle, sprue, runner, gate, key
They are emitted in the order of the cavities. Further here, on
One-stage sprue mold and two-stage sprue
It can be divided into blue molds, one-step blue molds
-It is also called a plate mold, and the sprue is only the first stage
The parting surface where the mold opens is one place,
The mold consists of two plates, a core and a cavity
I have. On the other hand, a two-stage sprue mold is a sleep rate mold.
It is said that the sprue has two stages and the molten resin is one stage
After passing through the sprue of the eye, the second stage via the runner
Through the sprue to the cavity
You. The mold here is core, cavity, sprue plate
Consists of three plates. Further, the above sprue, runner, and gate
To explain the general form, first, sprue is injected
From the part in contact with the molding machine nozzle to the runner
It is a resin passage and has a circular cross section. This sprue
Nozzle diameter is slightly smaller than the molding machine nozzle diameter.
It is designed to be large and the sprue must be
2 ° to 4 ° taper for easy pulling
Add a sprue lock such as a Z-shaped pin or reverse taper
Sometimes. Next, the runner is charged with molten resin as described above.
This is an intermediate passage from the prue to the gate.
The surface is circular or trapezoidal or semicircular. Especially many
In several molds, the arrangement of the cavity and runner is heavy.
It is important that the molten resin is
Must be designed to flow in. Also gate
Is the flow of molten resin from the runner into the cavity.
Although it is a mouth, it depends on the shape, appearance, quality, etc. of the molded product.
A gate has been devised. As the gate,
In addition to general direct gates, side gates,
Burlap gate, fan gate, film gate,
Disc gate, ring gate, tub gate, submarine
Gates, pinpoint gates, umbrella gates, etc.
Is known. [0005] By the way, the injection molding method as described above is used.
Some of the molded resin products are usually one-way molds
The mold cannot be opened and closed by the movement of
And a bowl-shaped article having a bottom portion. Where the bowl
The undercut part of the product has two main patterns
One of them is the thread end. That is, bowl-shaped
The thread end of the article gradually expands in the direction of the peripheral edge of the tip compared to the base.
And the other is a bowl-shaped object.
The bowl body diameter is designed to be larger than the opening diameter of the bowl body
If you are. On the other hand, it has a conventional undercut
When molding a molded resin article, for example,
(Regular pin) method is known. This structure is
A split core structure using a slide core for the mold.
When the pin is moved in the mold opening and closing direction,
The slide core moves vertically to the mold opening / closing direction.
The undercut can be cut out by moving
It is like that. In addition, the above-mentioned slide core
Actuators such as hydraulic cylinders and air cylinders
For moving small slide cores
Of the type that employs a cam guide or spring
Diagonally designed to pull out the undercut
A groove method and the like are known. However, these people
In the formula, the actuator for moving the movable mold
Besides the actuator, another actuator for moving the slide core
As the whole equipment becomes complicated, for example,
There was a problem that the size was increased. Thus, the present inventor has pointed out the point of improvement of the mold structure.
From Japanese Patent Application Laid-Open No. 10-166401
Mold for forming a bowl-shaped article having a
I tried to solve the problem. That is, JP-A-10-16
The invention according to No. 6401 has a strike between a fixed type and a movable type.
This is an injection mold with a ripper plate
Packing formed around cavities and inserts
After filling the packing material in the groove,
Bolt and bolt with play by bolt
At the same time, pack compressed air or pressurized liquid from outside
Into the inner lower surface of the collar of the nest, which is separated from the groove.
Injection molding dies characterized by having an introduction hole
there were. According to the injection mold, the undercut portion
Mold structure in mold for molding bowl-shaped article
It is not necessary to use a slide core, angular pin, etc.
It is not necessary to have a complicated mold structure with
Cylinder actuator for moving the slide core etc.
No additional driving means such as eta
It is possible to avoid overall complexity and enlargement.
Was. On the other hand, the present inventor has described the specification of the above-mentioned invention.
In the section of “action” and the section of “embodiment of the invention”,
Overview of injection molding based on the injection mold according to the above invention
However, as a result of subsequent research,
I found a problem to be improved. The problem is
According to the description of the embodiments of the invention,
In the process of mold release, first, the movable mold is
Is displaced downward, compressed air or pressurized
Liquid is delivered to the cavity plate and this compressed air
Or pressurized liquid lowers the cavity plate
Is pushed down. Here, the package enclosed in the packing groove
The packing member is restored and the inside of the packing groove
Seal the space between the cavity and the cavity plate.
Pressurized by compressed air or pressurized liquid
The bottom of the inside of the thread end of the molded bowl-shaped article
And the compressed air or pressurized liquid
Yarn formed as undercut by pressure action
Press out from the cavity plate without damaging the buttocks
Could be done. However, in this state,
The molded bowl-shaped article is attached to the core and the movable mold is
The movable type retreats and moves.
The protruding lot moves upward when displaced to the home position,
Return pin tip protrudes below stripper plate
And the molded bowl-shaped article is separated from the core
there were. Also, according to this method, the undercut portion is
It should be able to mold resin bowl-shaped articles in good condition.
Was confirmed. [0008] However, subsequent continuous experiments and research
As a result, the undercut in the body of the resin bowl-shaped article
Large, so-called cloth bag shape is remarkable,
While applying uneven carving patterns to the molding surface of the bowl-shaped article,
That is, the core of the injection mold and the cavity plate are concave.
A convex pattern is engraved and the underbody is
When molding a resin bowl-shaped article having a
The movable mold is separated from the fixed mold and made of resin when the mold is opened.
The so-called hugging effect on the core of the bowl-shaped article is large,
Open the mold while the resin bowl-shaped article after forming is strongly attached to the core
It was displaced in the direction. According to this, the resin
Bowl-shaped articles are punched out of the cavity plate to some extent
The resin bowl is separated from the core in the
The product cuts into the edge-like parting line and the bowl
Cracks at the outer opening edge of the
There is a drawback that the product cannot be designed,
Was. Therefore, the present invention addresses the above-mentioned problems of the conventional technology.
It has been made in view of the
It is based on the knowledge obtained through research and experiments.
The intended purpose is to attach an undercut to the thread end of the bowl-shaped article.
With a large undercut on the torso
So-called cloth bags, mold cores, cavities
An uneven pattern is engraved on the plate and the torso
Injection molding of resin bowl-shaped article with undercut part
However, cracks may occur at the outer opening edge of the bowl-shaped article,
Or there is no problem such as not being able to obtain the shape as designed,
An injection molding method for a bowl-shaped article having an undercut portion is provided.
To provide. [0009] To achieve the above object,
Of a bowl-shaped article having an undercut according to the present invention.
The injection molding method has the following configuration. That is, in the present invention
Injection molding method for bowl-shaped articles having such undercut portions
Fills the molten resin into the cavity of the clamped mold
After waiting for the resin to cool and harden, open the mold.
In the injection molding method for obtaining a resin molded product by performing
Are the fixed type that defines the outer part of the bowl-shaped article and the inside of the bowl-shaped article.
Between the movable mold that defines the side and the fixed mold and the movable mold
A molding die provided with a stripper plate,
Extends outward from the top of the main body and forms a flange
The inner surface of the yarn end of the bowl-shaped article and the pinpoint game
The lower surface of the nested collar that defines the bottom inside the thread end
And the lower surface of the flange of the nest comes into contact with the bowl, and
Cavity plate that defines the outer surface of the body and the outer surface of the thread end
The packing grooves are engraved on the upper surface, and the packing
While the packing member is sealed in the groove,
The flange is bolted with play with the cavity plate.
The cavity plate.
Engraved packing groove on the lower surface of the collar formed on the scribe
Compression from outside of the machine at the inner flange lower surface position more separated
An injection hole for introducing gas or pressurized liquid
Using a die for molding
And the runner in contact with the upper surface of the cavity plate
Stripper plate and the runner strip
On top of par plate and runner stripper plate
Connect the fixed side mounting plate that is in contact with the parting lock mechanism
And there is a limit switch when opening the mold
Or mold opening including electrical control circuits such as position sensors.
By operating the closing control device, first the core in the mold
To stop temporarily, and then move up from the introduction hole.
Pressurized gas or pressurized between cavity plate and insert
Inject the liquid and cool and cure the resin molded product in the cavity
Press out from the plate and attach it to the core on the opposite side,
Subsequently, the mold opening is restored and the core is further retracted.
On the other hand, due to the displacement limitation of the movable mold,
Between the runner stripper plate and the runner
The part between the stripper plate and the fixed side mounting plate
It is necessary to release the connection of the locking lock mechanism.
To the effect. As described above, Japanese Patent Application Laid-Open No. Hei 10-1
In No. 66401, the movable mold is placed below the fixed mold.
At the same time, the compressed air or
The structure is such that the pressurized liquid is delivered to the cavity plate
I was Because of this configuration, the body of the bowl-shaped article
Large undercut, so-called cloth bag shape is remarkable
For products, the molded resin bowl-shaped article has a strong core.
Since it is displaced in the mold opening direction with it attached,
A bowl-shaped article cuts into the edge-like parting line
As a result, a crack occurred at the outer opening edge of the bowl-shaped article.
Or defective molding without obtaining the originally designed shape
There was that. Therefore, in the present invention,
As in the configuration, when the mold is opened, the limit switch
Switch or an electrical control circuit such as a position sensor
By the operation of the mold opening and closing control device, the resin molded product in the mold
With the movable mold plate remaining on the fixed mold cavity plate.
After temporarily displacing the core down, stop it temporarily.
Pressurized gas or pressurized liquid from outside the machine
The resin bowl-shaped article is injected between the nest and
Elastic deformation inside opening due to punching from side
Can be restored after the extrusion
Molded by the parting edge of the bitty plate
The shearing force acting on the opening edge of the resin bowl-shaped article
The edge-shaped par of the resin bowl-shaped article.
It is possible to eliminate biting into the
Acts to be able to. Next, a compressed gas or pressurized liquid from outside the machine
The body is inserted through the introduction hole formed in the cavity plate.
Set to be injected between the cavity plate and nest
The compressed gas or pressurized liquid is
To push up the lower surface of the flange. This allows the
Mutually provided on the upper surface of the bitty plate and the lower surface of the nest flange
The packing groove has a play width for releasing the contact and bolting.
Packing member, which is enclosed in the packing groove
Is restored while being pinched in the packing groove, and the packing is
Seal the separation space inside the groove, and pressurize the
To maintain pressurization by compressed gas or pressurized liquid.
You. Thus, the inner surface of the yarn end of the resin bowl-shaped article and
Pressurizing the inner surface of the yarn end with the above compressed air or pressurized liquid
To form a resin bowl-shaped article with an undercut.
Pushed out of the cavity plate, facing away
Attach it to the movable core. Subsequently, when the movable mold further retreats downward,
The storage mold is a stage where the downward separation of the movable mold exceeds a predetermined displacement.
And are connected by a parting lock mechanism
Note cavity plate and runner stripper play
G, Runner stripper plate and fixed side mounting plate
Is disconnected. Furthermore, the movable mold continues to move downward
When it reaches the predetermined position, it moves the protruding rod upward
And the protruding plate on which the return pin is planted protrudes.
The return pin projects from the lower surface of the stripper plate.
And the stripper plate is projected upward
It acts to separate the resin bowl-shaped article from the core. BRIEF DESCRIPTION OF THE DRAWINGS FIG.
The present invention continues through the preferred embodiments of the present invention.
Will be described in detail. First, FIG. 1 shows an undercut according to the present invention.
Attach a mold for molding bowl-shaped articles with a part to an injection molding machine
Cross section of the molding die when the mold is clamped and the injection is completed
FIG. As shown, a molding die 1 according to the present invention
Is formed with the fixed mold 2 defining the outer portion of the molded bowl-shaped article 28.
A gap is formed between the movable mold 3 defining the inside of the bowl-shaped article 28.
With the tosper plate 4 interposed,
Between the fixed side mounting plate 12 and the runner stripper plate 13
And runner stripper plate 13 and cavity
Between the plate 14 and the parting lock body 32
Parting lock consisting of a retaining lock insertion part 33
With the mechanism interposed, the movable mold plate 8 and the cavity
Plate 14 and runner stripper plate 1
3 and the cavity plate 14 are connected with the tension link 34 and
The connecting mechanism is interposed by the tension link retainer 35.
It is a thing. Further, as shown in FIG.
It can be moved up and down by a heater (not shown) and
A movable-side mounting plate 6 having a pad play insertion hole 5;
Spacer block 7 fixed to upper surface of attachment plate 6 and movable
The movable mold plate 8 which is disposed above the side mounting plate 6 and is described later
Slidably penetrates and the tip is on the lower surface of stripper plate 4
Projection plate 10 with return pin 9 in contact with it
And further fixed on the upper surface thereof through a spacer block 7.
The movable mold plate 8 to be fixed and the upper surface of the movable mold plate 8
To define the inner surface of the bowl body 29 of the molded bowl-shaped article 28
A core 11 is provided. On the other hand, the fixed type 2
Is a runner strike disposed on the lower surface of the fixed-side mounting plate 12.
Ripper plate 13 followed by runner stripper
The molded bowl-shaped article 28 is disposed on the lower surface side of the plate 13.
A cap defining the outer surface of the bowl body 29 and the outer surface of the thread end 30
Between the cavity plate 14 and the cavity plate 14
It is inserted from the upper surface side and extends outward from the upper surface of the telescopic body 15.
The nested collar portion 16 is formed by being extended around the cavity.
A flat upper surface is formed together with the upper surface of the plate 14, and
The inner bottom surface and the inner side surface of the thread end 30 of the bowl-shaped article 28 are defined.
Nest 17. Here, the fixed side mounting plate
The tip of the injection nozzle (not shown) is brought into close contact with the upper surface of 12
The contact recess 18 is formed and the contact recess 18 is formed.
The sprocket penetrates vertically from the center to the lower surface of the fixed side mounting plate 12.
A sprue hole base 20 that forms a part of the roux 19 is drilled
The sprue hole base 20 is connected downward and the runner
The stripper plate 13 also
A sprue hole body 21 that forms a part of the
And further connected downwardly to the sprue hole body 21.
The sprue extends from the upper surface to the vicinity
A sprue hole head 22 that forms a part of 19 is drilled,
Subsequently, between the tip of the sprue hole head 22 and the lower surface of the insert 17
, A pin point gate 23 is formed. Illustrated on the other side
As shown in FIG.
Abuts on the lower surface of the nest 16 of the child 17 and the nest 16
Mutually engraved on the upper surface of the cavity plate 14
Rubber packing member 2 on ring in packing groove 24
5 is enclosed, and the nest 17 of the nest 17
Bolt 2 planted with tea plate 14 and play
It is inserted by being bolted with 6. Ma
The cavity plate 14 has compressed air from outside the machine.
Is engraved around the lower surface of the nest 16 formed on the nest 17.
Below the inner nest collar 16 which is separated from the packing groove 24
An introduction hole 27 for introducing into the surface position is formed. More than
Bowl-shaped article having such an undercut according to the present invention
The molten resin injection-molded in the molding die of
Cooled and hardened by flowing into the molding space from the int gate 23
Is done. Here, the molded bowl-shaped article 28 is a bowl-shaped article.
Depends on the shape of the undercut on the thread end and body
And is usually used for injection molding such molded articles.
Is how to open the mold by using elements such as angular pins
The mold so that the mold slides perpendicular to the
Needed to be Next, FIG. 2 shows a molding die according to the present invention.
It is sectional drawing which showed the 1st process in opening. here,
In this first process, the movable mold 3 is
Displaced downward, shaped bowl with undercut
The article 28 remains in the fixed mold 2 and
The inner surface of the bowl body 29 of the bowl-shaped article 28 is defined.
The movable die 3 including the core 11 retreats below a predetermined range. FIG. 3 shows a mold of a molding die according to the present invention.
It is sectional drawing which showed the 2nd process in opening. The above
If the movable mold 3 retreats below the predetermined range in one process,
These compressed airs were perforated in the cavity plate 14.
It is sent out from the introduction hole 27. This
Therefore, the compressed air sent out is caused by the downward displacement of the movable mold 3.
A cavity preform is formed at the nest collar 16 of the nest 17.
Bolt 14 with play and with bolt 26
Since it is inserted and inserted,
Provided on the upper surface of the bite plate 14 and the lower surface of the nest collar 16
The mutual packing grooves 24 are released from contact with each other,
But the rubber sealed in the packing groove 24
The packing member 25 is formed in the packing groove 2 together with the separation.
4 and is restored.
Seals the space inside the engraved packing groove 24
Then, pressurization by compressed air sent from outside the machine is maintained. This
Thus, the yarn end 3 of the molded bowl-shaped article 28 formed by cooling and hardening is formed.
Pressing the inner bottom surface and the inner side surface of the thread end 30 with the compressed air
As an undercut portion of the molded bowl-shaped article 28
Good cavity without damaging the formed thread end 30
-It can be pushed out from the plate 14 and
Of the resin bowl-shaped article 28 after molding
Even if an undercut part is formed in the part,
1 is retreated downward, the shaped bowl-shaped article 28
After elastic deformation inside the opening and accompanying its extrusion
It can be restored and, needless to say, is strongly attached to the core 11.
And cut into the edge-like parting line.
Because there is no possibility of opening, the inside of the opening of the molded bowl-shaped article 28
Cracks may occur at the rim, or the originally designed shape
It does not mean that it is not formed without being defective. Also here
Then, the molded bowl-shaped object punched out from the fixed side 2 as described above
The article 28 is extruded by the above pressure and adheres to the core 11.
State. Furthermore, the vertical play of the bolting
The width can be set to 1 to 2 mm, and compressed air from outside
1 ~ 10kg square centimeter can be set
You. The delivery of the compressed air is performed by the cavity press.
The molded bowl-shaped article 28 is punched out from the sheet 14 and the core 1
It can be stopped at the stage where it is attached to 1,
Use a well-known timer control, etc. for stop control
Can be. Subsequently, FIGS. 4 and 5 respectively show the present invention.
Sectional view showing the third step in opening the molding die.
FIG. 4 is a diagram showing a fourth example of opening of the molding die according to the present invention.
It is sectional drawing which showed the process. Fixed as shown in Fig. 3 above
The molded bowl-shaped article 28 punched from the mold 2 side is attached to the core 11.
Retreats downward while adhering, moves away from the fixed mold 2 side by a predetermined range
When separated, a gap is formed between the cavity plate 14 and the movable mold plate 8.
Existing tension link 34 and tension link retainer
When the movable mold 3 is retracted downward, the
The fixed mold 2 will follow the fixed distance.
However, as shown in FIG.
The path interposed between the inner stripper plates 13
Parting lock body 32 and parting lock insertion
The parting lock mechanism consisting of the part 33 is released,
Only the cavity plate 14 and insert 17 on the mold 2 side
Follows the retreat of the movable mold 3. Furthermore, figure
5 is a case where the movable mold 3 subsequently retreats downward.
Then, the movable mold 3 further retreats downward from the state of FIG.
The cavity plate 14 that follows the movable mold 3 is fixed
Runner stripper plate 1 staying in standard 1
When the distance between the three reaches a predetermined separation range, the cavity gap
Between the rate 14 and the runner stripper plate 13
Existing tension link 34 and tension link retainer
When the movable mold 3 is retracted downward, the
The robot will follow with a fixed separation distance.
Secure with runner stripper plate 13 as shown
Parting lock book interposed between the side mounting plates 12
The par consisting of the body 32 and the parting lock insertion part 33
The locking lock mechanism is released and the fixed type 2 side runner
The stripper plate 13 also accompanies the retraction of the movable mold 3.
Become like Here, the sprue 19 is run as shown.
Pull out while remaining on the nurse stripper plate 13
I will be able to be. FIG. 6 shows a molding metal according to the present invention.
It is sectional drawing which showed the 5th process in the mold opening of a type | mold.
The movable mold 3 further retreats further downward from the state of FIG.
When it reaches the position, the protruding rod 31 moves upward.
So that the return pin 9 is planted.
The provided extension plate 10 projects upward.
You. Next, the tip of the return pin 9 is
Protruding the lower surface of the sheet 4 and forming a
The article 28 is detached from the core 11. The present invention is configured as described in detail above.
Has the effects described below.
You. A bowl having an undercut according to the present invention
According to the injection molding method for a shaped article, the mold structure for molding is specially designed.
Special split-type structure with separate cylinder actuator
Slide core and angular pin
Without the need for complicated mechanisms such as
It has an undercut at the end of the thread and
A resin bowl with a large undercut and a remarkable cloth bag shape
Products, injection molding die core, cavity play
And the underside of the body
-Injection molding of resin bowl-shaped articles with cut parts
There is an effect that can be cut. In addition to the above effects, a mold structure and
Molding without complicating the mold opening mechanism of the mold
In addition to reducing product costs, injection molding
High operating reliability of equipment and high yield of molded products
There is also an effect that can be.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a mold for molding a bowl-shaped article having an undercut portion according to the present invention attached to an injection molding machine, which is closed when the mold is clamped and the injection is completed. Sectional view. FIG. 2 is a sectional view showing a first step in opening the molding die according to the present invention. FIG. 3 is a cross-sectional view showing a second step in opening the molding die according to the present invention. FIG. 4 is a cross-sectional view showing a third step in opening the molding die according to the present invention. FIG. 5 is a sectional view showing a fourth step in opening the molding die according to the present invention. FIG. 6 is a sectional view showing a fifth step in opening the molding die according to the present invention. DESCRIPTION OF SYMBOLS 1 Molding mold 2 according to the present invention 2 Fixed mold 3 Movable mold 4 Stripper plate 5 Rod insertion hole 6 Movable mounting plate 7 Spacer block 8 Movable mold plate 9 Return pin 10 Projection plate 11 Core 12 Fixed side mounting plate 13 Runner stripper plate 14 Cavity plate 15 Nested body 16 Nested flange 17 Nested 18 Contact recess 19 Sprue 20 Sprue hole base 21 Sprue hole body 22 Sprue hole head 23 Pinpoint gate 24 Backing Groove 25 Packing member 26 Bolt 27 Inlet hole 28 Molded bowl-shaped article 29 Bowl body 30 Thread end 31 Projecting rod 32 Parting lock insertion part 33 Parting lock body 34 Tension link 35 Retainer for tension link

Claims (1)

(57) [Claims] [Claim 1] After filling a molten resin into a cavity of a clamped mold, the mold is opened after cooling and curing of the resin to obtain a resin molded product. In the injection molding method,
The mold is a fixed mold that defines the outer part of the bowl-shaped article, a movable mold that defines the inner part of the bowl-shaped article, and a molding tool that has a stripper plate interposed between the fixed mold and the movable mold. A mold extending outward from the upper surface of the main body, forming a flange around the inner periphery, and defining an inner surface of the yarn end of the bowl-shaped article and an inner bottom surface of the yarn end where a pinpoint gate is formed. The lower surface of the collar portion and the lower surface of the collar portion of the nest are in contact with each other, and packing grooves are formed on the upper surface of the cavity plate defining the outer surface of the bowl body and the outer surface of the thread end of the bowl-shaped article. While the packing member is sealed in the groove, the flange of the insert is bolted and inserted with play with the cavity plate, and the cavity plate has a peripheral surface of a lower surface of the flange formed on the insert. More spaced than engraved packing groove An injection molding die having an introduction hole for introducing a compressed gas or a pressurized liquid from outside the machine is used at the lower surface of the inner flange portion, and the cavity plate in the mold and the upper surface of the cavity plate are used. The abutting runner stripper plate is further connected to the runner stripper plate and a fixed-side mounting plate abutting on the upper surface of the runner stripper plate by a parting lock mechanism. When the mold is opened, an electric switch such as a limit switch or a position sensor is provided. Of the mold opening / closing control device including the dynamic control circuit, the core in the mold is first displaced downward and then temporarily stopped, and then compressed between the cavity plate and the insert through the introduction hole. Inject gas or pressurized liquid, and cool and cure resin molded product from cavity plate to face The mold is then reopened and the core is further retracted, while the displacement of the movable mold is restricted between the cavity plate and the runner stripper plate, and then the runner stripper plate and the fixed side. An injection molding method for a bowl-shaped article having an undercut portion, wherein the connection of the parting lock mechanism between the mounting plates is released.