JPH0911270A - Blow injection molding device - Google Patents

Abstract

PURPOSE: To separate, in a mold, an excessively thick part which is solidified in an auxiliary cavity. CONSTITUTION: A movable block 29 to be moved up and down by a cylinder device 28 is arranged in an auxiliary cavity 23 provided in an arrangement communicating with a product cavity 3. In a state that the movable block 29 is made to proceed so as to reduce the capacity of the auxiliary cavity 23, a melted resin is injected into the product cavity 3 and a part of the auxiliary cavity 23. Thereafter, by conforming with injection of high-pressure fluid into the melted resin in the product cavity 3, the movable block 29 is backed so as to expand the auxiliary cavity 23. By making a part of the melted resin flow from the product cavity 3 to the auxiliary cavity 23, a hollow is formed. After it is solidified, when a molding is to be extruded by rise of an extruded sheet 33, an auxiliary extruder pin 35 at the auxiliary cavity 23 is moved relatively to an extruder pin 14 at a molding body and an excessively thick part which is solidified in the auxiliary cavity 23 is pressed down by a proper fixing means so as to separate from the molding body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hollow injection molding apparatus for injection molding a hollow molded body.

[0002]

2. Description of the Related Art In hollow injection molding, a pressurized fluid is usually injected into a molten resin injected into a cavity, and the pressure of the pressurized fluid pushes the molten resin into the cavity to form a hollow portion. At this time, a part of the molten resin is caused to flow to a sub-cavity provided in communication with the cavity (product cavity) to assist the formation of the hollow portion.

9 and 10 show an example of an injection molding die for performing such molding. In these figures, 1 is a fixed mold for fixing the position, 2 is a movable mold which is arranged so as to be able to approach and separate from the fixed mold 1. Has a cavity (product cavity) 3 formed therein. A sprue bush 5 having a sprue 4 is fitted in the fixed die 1, and a molten resin is injected into the product cavity 3 through a sprue 4 from an injection nozzle (not shown) of a molding machine connected to the rear end of the sprue bush 5. Will be emitted. Then, in the mating portion of the fixed mold 1 and the movable mold 2,
A sub-cavity 7 that communicates with the product cavity 3 through a communication passage 6 is provided. This sub-cavity 7 is provided by a recess 1a provided in the fixed die 1 and a through hole 2a provided in the movable die 2, and the through hole 2a is provided by a cylinder device 8 attached to the back surface of the movable die 2. A movable block (plug) 9 that is driven up and down is slidably arranged.

In order to perform hollow injection molding using the above-mentioned mold, after closing the movable mold 2 on the fixed mold 1, the movable block 9 is moved upward by the operation of the cylinder device 8 to move the auxiliary cavity 7 and the product cavity. 3 is closed (FIG. 9), and molten resin is injected into the product cavity 3 through the sprue 4. Then, after the injection of this molten resin is completed,
For example, a pressurized fluid is injected into the molten resin in the product cavity 3 through a fluid nozzle incorporated in the injection nozzle, and the movable block 9 is moved downwardly before and after this to open the communication passage 6. Then, the molten resin spreads in the product cavity 3 and sticks to the molding surface, and at the same time, a part thereof flows into the sub-cavity 7 from the communication passage 6 to form a hollow portion 10 having a predetermined size (FIG. 10). . A similar molding method is disclosed in JP-A-5-9.
It is also disclosed in Japanese Patent No. 6560.

According to such a molding method, by closing the communication passage 6 first, the molten resin inadvertently flows into the sub-cavity 7 before the molten resin is sufficiently turned into the product cavity 3. In addition, by adjusting the moving amount of the movable block 8 and changing the volume of the sub-cavity 7, even if the amount of molten resin flowing out into the sub-cavity changes due to changes in molding conditions, etc. The change can be easily dealt with, and the molded body 11 (FIG. 11) having the hollow portion 10 having a predetermined size can be stably molded.

After the above-mentioned molding is completed, as shown in FIG. 11, the movable die 2 is separated from the fixed die 1 (the die is opened), and the extruding plate (not shown) is moved to raise the extruding pin 14. The molded body 11 is extruded from the movable mold 2. At this time, the molded body 11 has a columnar protrusion 1 as a part that is removed from the sprue 4.
2 and a surplus portion 13 solidified in the sub-cavity 7 are attached to the outside of the mold by, for example, advancing and retracting the work take-out device (not shown) arranged around the mold into and out of the mold. Be delivered to.

[0007]

However, according to the injection molding apparatus which utilizes the above-mentioned sub-cavity 7 to assist the formation of the hollow portion, the molded body 11 has the extra-thickness portion solidified in the sub-cavity 7. Since 13 is connected, after the molded body 11 is carried out of the mold, the surplus portion 1 is removed from the molded body 11.
There is a problem that a cutting step for separating 3 is required, and that cutting requires a troublesome procedure, and it is inevitable that productivity is deteriorated and manufacturing cost is increased.

The present invention has been made in view of the above problems, and its object is to make it possible to divide the surplus portion solidified by the sub-cavity in the mold, thereby improving the productivity. An object of the present invention is to provide a hollow injection molding device that greatly contributes to reduction of manufacturing cost.

[0009]

In order to solve the above-mentioned problems, the present invention provides a mold provided with a sub-cavity in communication with a product cavity, in which a movable block for varying the volume of the sub-cavity is incorporated. A hollow is formed by injecting a pressurized fluid into the molten resin injected into the product cavity to form a hollow portion while allowing a part of the molten resin to flow out to the sub-cavity, and extruding a molded body with an extrusion pin. The injection molding apparatus is characterized in that a fixing means for fixing the excess thickness portion solidified in the sub-cavity is provided against the extrusion of the molded body by the extrusion pin.

According to the present invention, the fixing means may be provided in a work taking-out means for taking out a molded product from a mold. Further, the fixing means may be configured to share the movable block.

Further, the present invention further comprises a sub-extrusion pin for extruding a surplus portion solidified in the sub-cavity, the sub-extrusion pin being a two-stage extrusion in which the sub-extrusion pin is operated with a time lag from the extrusion pin. Connected to the extrusion plate through the mechanism,
The fixing means may be formed of a locking portion that is provided at a tip portion of the auxiliary extrusion pin and that locks the extra thickness portion.

[0012]

In the hollow injection molding apparatus configured as described above, when the molded body is extruded by the extrusion pin after injection molding,
By fixing the excess thickness portion by the fixing means, a shearing force acts on the connecting portion between the molded body and the excess thickness portion, and the excess thickness portion is separated from the molded body.

Further, when the fixing means is provided in the work take-out means, not only the excess thickness portion can be fixed by utilizing the movement of the work take-out means, but also the divided molded body is automatically removed by the work take-out means. It can be taken out of the mold. Also,
When the fixing means is also used as the movable block, the movable block can be operated with the mold half-opened to fix the extra thickness portion.

Further, when the fixing means is formed of a locking portion provided on the auxiliary extrusion pin connected to the extrusion plate through the two-stage extrusion mechanism, the auxiliary extrusion pin operates with a time lag from the extrusion pin, A shearing force acts on the connection between the extra thickness portion locked by the locking portion at the tip of the auxiliary extrusion pin and the molded body extruded by the extrusion pin.

[0015]

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

1 to 5 show a hollow injection molding apparatus according to the present invention. It should be noted that FIGS. 9 and 10 described above are used.
The same parts as the parts shown in are denoted by the same reference numerals, and the description thereof will be omitted here. In the present embodiment, the movable die 2 is attached via a spacer 21 to a mounting plate 20 which is driven up and down by a driving means (not shown).
It moves upward together with 0 and is fitted to the fixed mold 1. In addition, a sub-cavity 23 that communicates with the product cavity 3 via a communication passage 22 is provided at the mating portion of the fixed die 1 and the movable die 2.

The sub-cavity 23 has a first chamber 24 extending along a parting surface of the fixed mold 1 and the movable mold 2, and second and second chambers extending from the first chamber 24 to the rear side of the fixed mold 1. Three
Chambers 25 and 26, each of which is provided by a recess and a hole formed in the fixed mold 1. Second chamber 25
Has a larger volume than the third chamber 26, and a movable block 27 is slidably installed therein. The movable block 27 is connected to the tip of a rod 29 extending from a cylinder device 28 arranged on the back surface of the fixed mold 1.
The cylinder device 28 includes a cylinder body 31 in which a piston 30 that supports the base end of the rod 29 is slidably mounted. By supplying / discharging pressurized oil or compressed air into / from the cylinder body 31, the rod 29 expands / contracts, and accordingly the movable block 27 moves up and down to move the second chamber 25.
Is changed, and as a result, the total volume of the sub-cavity 23 is changed. The escape portion 26 has a columnar shape, and like the sprue 4, has a tapered shape in which the diameter decreases toward the rear surface side of the fixed mold 1.

In injection molding, a fixed mold 1 and a movable mold 2 are used.
After closing, the movable block 27 is moved forward (downward) by the operation of the cylinder device 28, the communication between the second chamber 25 and the first chamber 24 forming the sub-cavity 23 is cut off, and the sub-cavity 23 is closed. With the total volume reduced (FIG. 1), molten resin is injected into the product cavity 3 through the sprue 4. Then, a part of this molten resin flows into the sub-cavity 23 from the communication passage 22, and the first chamber 24 and the third chamber 2
And 6 are filled. After the injection of the molten resin is completed, a pressurized fluid is injected into the molten resin in the product cavity 3 through, for example, a fluid nozzle incorporated in the injection nozzle.
The sub-cavity 23 is expanded by retreating by the operation of 8 (FIG. 3). As a result, the molten resin spreads in the product cavity 3 and sticks to the molding surface, and a part of it melts into the communication passage 2
2 flows into the second chamber 25 in the sub-cavity 23,
A hollow portion 10 having a predetermined size is formed.

As described above, first, the molten resin is also filled in the first chamber 24 and the third chamber 26 in the sub-cavity 23, so that the molten resin is inadvertently transferred from the product cavity 3 to the sub-cavity 23. The amount does not flow out, and moreover, by adjusting the amount of movement of the movable block 27 and changing the volume of the sub-cavity 23, it is possible to easily deal with changes in molding conditions, etc. The molded body 11 (FIG. 5) that it has can be stably molded.

By the way, in the space 32 between the movable die 2 and the mounting plate 20 which is separated by the spacer 21, the extruding plate 33 which supports the extruding pin 14 which extends through the movable die 2 and extends in the vertical direction. Are arranged. The pushing plate 33 is connected to a plurality of operating rods 34 extending from the pushing driving means (not shown) arranged below the mounting plate 20 through the mounting plate 20 and operating upward by the pushing driving means. It is adapted to move up and down in the space 32. In addition,
The push-out plate 33 is composed of two upper and lower plate bodies 33a and 33b, and these two plate bodies 33a and 33b are integrally combined by fastening means (not shown).

The extruding pin 14 is arranged corresponding to the product cavity 3 as in the conventional case, while the auxiliary extruding pin 35 is arranged corresponding to the sub-cavity 23 separately. The extrusion pin 14 is directly connected to the extrusion plate 33, while the auxiliary extrusion pin 35 is connected to the extrusion plate 33 via a two-stage extrusion mechanism 36. As shown in FIG. 4, the two-stage extrusion mechanism 36 includes two plate members 33a, 3a of the extrusion plate 33.
3b is provided with a common cylinder portion 37, and the base end large diameter portion 38 of the sub-extrusion pin 35 is provided in the cylinder portion 37.
And a large-diameter upper end portion 40 of the stopper member 39 projecting downward from the push-out plate 33. The length of the cylinder portion 37 is set to be longer than the value obtained by adding the thickness of the proximal large diameter portion 38 of the auxiliary extrusion pin 35 and the thickness of the upper large diameter portion 40 of the stopper member 39 by the distance S. There is. Therefore, the auxiliary push-out pin 35 can move relative to the push-out pin 14 by the amount of S.

The large-diameter portion 38 of the base end of the auxiliary push-out pin 35 and the large-diameter portion 40 of the upper end of the stopper member 39 located inside the cylinder portion 37 are always seated on the bottom of the cylinder portion 37 due to their own weight. (The state shown by the solid line in FIG. 3) is maintained, and in this state, the stopper member 39 projects from the lower surface of the pushing plate 33 by the distance L. The stopper member 39 is the push plate 3
As the protrusion 3 descends, its protruding end abuts on the mounting plate 20 and receives pressure from the mounting plate 20 to move upward. The protrusion length L of the stopper member 39 is set so that the stopper member 39 is pushed by the mounting plate 20 and moves upward by the distance S when the pushing plate 33 is positioned at the lower end. Therefore, at the lower end of the push-out plate 33, the large-diameter portion 39 of the sub-extrusion pin 35 and the large-diameter portion 40 of the upper end of the stopper member 39 are positioned so as to be seated on the ceiling of the cylinder portion 37. Therefore, the length of the sub-extrusion pin 35 is set so that the upper end thereof is just flush with the upper surface of the movable die 2 at the rising end of the base end large diameter portion 39. At the descending end, the upper end of the auxiliary extrusion pin 35 is positioned so as to be flush with the upper surface of the movable die 2. The length of the extruding pin 14 is also set so that the upper end of the extruding plate 33 is exactly flush with the upper surface (molding surface) of the movable die 2 at the lower end.

Here, a work take-out device 41 as shown in FIG. 5 is arranged around the die including the fixed die 1 and the movable die 2. This work take-out device 41 is provided with an arm 42 which is movable between a fixed mold 1 and a movable mold 2, which are opened, and which can move up and down and can move up and down. At the tip of the arm 42, a first clamp device 43 that detachably holds the molded body 11 and a second clamp device that detachably holds the excess thickness portion 15 solidified in the sub-cavity 23 are provided. And 44 are provided. First clamp device 43
Is a hollow holder 45 having at its lower end an insertion hole for the columnar protrusion 12 as the above-mentioned dropout portion of the sprue 4, and a pressing member for fixing the columnar protrusion 12 mounted in the holder 45 into the insertion hole of the holder 45. And a cylinder device 47 having a member 46 at the rod end.

On the other hand, the second clamp device 44 has a hollow holder 4 having an insertion hole at the lower end into which the columnar protrusion 16 solidified in the third chamber 26 in the sub-cavity 23 can be inserted.
8 and a pressing member 49 attached to the holder 48 for pressing and fixing the columnar protrusion 16 in the insertion hole of the holder 48.
And a cylinder device 50 having a rod end.
It should be noted that the extra thickness portion 15 has a second portion in the sub-cavity 23.
A protrusion 17 solidified in the chamber 25 is also provided.

In this embodiment, after the injection molding is completed, the movable die 2 is moved downward together with the mounting plate 20 to separate it from the fixed die 1, and then the arm 42 of the work take-out device 41 is inserted between the two. . At this time, the pressing members 46 and 49 of the first and second clamp devices 43 and 44 are retracted to the unclamp position by the operation of the cylinder devices 47 and 50. Then, the arm 42 is lowered at a predetermined entry position, and the holder 4 of the first and second clamp devices 43 and 44 is moved.
Corresponding columnar protrusions 13 and 16 are inserted into the holes 5 and 48. Next, when the columnar projections 13 and 16 are inserted to an appropriate depth, the lowering of the arm 42 is stopped, the cylinder device 50 of the second clamp device 44 is operated, and the pressing member 49 at the tip thereof is advanced. The columnar protrusions 16 associated with the extra thickness portion 15 are clamped.

After the columnar protrusions 16 in the extra thickness portion 15 are clamped, the pushing plate 33 is raised by the driving means.
Then, since the push-out pin 14 corresponding to the molded body 11 is directly connected to the push-out plate 33, the push-up pin 14 rises integrally with the push-out plate 33, whereby the push-out force (lifting force) is exerted on the molded body 11 from the push-out pin 14. ) Is added. On the other hand, the auxiliary extrusion pin 35 corresponding to the extra thickness portion 15 is supported by the extrusion plate 33 so as to be capable of floating via the two-stage extrusion mechanism 36, so that the base end large diameter portion 38 of the auxiliary extrusion pin 35 and the stopper member. The upper-end large-diameter portion 40 of 39 moves down the inside of the cylinder portion 37 by the distance S as the push-out plate 33 rises. That is, while the push-out plate 33 is raised by the distance S, the push-out pin 14 and the sub-extrude pin 35 move relative to each other, and the lifting force of the sub-extrude pin 35 is applied to the surplus portion 15 solidified in the sub-cavity 23. Does not work. At this time, the extra thickness portion 1
Since 5 is clamped by the second clamp device 44, a shearing force acts on the connecting portion between the molded body 11 extruded by the extruding pin 14 and the position-fixed excess thickness portion 15, and the excess thickness portion 15 Are separated from the molded body 11.

The push-out plate 33 continues to rise even after the above-mentioned division, and the arm 42 also rises accordingly. And
When the arm 42 moves up to a predetermined position, the cylinder device 47 of the first clamp device 43 is actuated to press the pressing member 46.
Is advanced to clamp the columnar protrusion 46 attached to the molded body 11. The second clamp device 44 is already provided with the excess thickness portion 15
Are clamped, and the push-out plate 33 descends, and at the same time, the arm 42 retreats, whereby the molded body 11 and the surplus portion 1
It is taken out of the mold while being separated from 5. After that, the arm 42 is rotated by the operation of the arc extracting device 41,
For example, the molded body 11 is discharged to a predetermined molded body storage space, and the surplus portion 15 is discharged to a predetermined scrap storage space, whereby the molding of one hollow molded body is completed.

In the present embodiment, in particular, the auxiliary extruding pin 35 for extruding the excess thickness portion 15 is supported by the extrusion plate 33 in a floating manner, and the clamp device 44 as a fixing means for fixing the excess thickness portion 15 is taken out of the work. Since the device 41 is provided, the excess thickness portion 15 is divided from the molded body 11 by the relative movement of the auxiliary extrusion pin 35 and the extrusion pin 14 for extruding the molded body, and the divided molded body 11 and the excess thickness portion 15 are separated. The part 15 and the part 15 can be automatically taken out of the mold by the work taking-out means, and continuous molding is possible, and the productivity is greatly improved. Further, since the columnar protrusion 16 having a constant shape is provided in the extra thickness portion 15,
Clamping by the second clamp device 44 becomes reliable, and the work taking out work is stabilized.

In the above embodiment, the stopper member 39 is used as the two-stage pushing mechanism 36, and the sub pushing pin 35 is used.
However, a spring (not shown) is used in place of the stopper member 39, and this spring is arranged in the cylinder portion 37 so that the proximal large-diameter portion 38 of the sub-extrusion pin 35 is provided.
May be always biased upward. Further, the two-stage pushing mechanism 36 can be configured as a whole as a fluid pressure cylinder. In this case, the stopper member 39
Is closed to close the bottom of the cylinder portion 37, and the proximal large-diameter portion 38 of the sub-extrusion pin 35 is used as a piston to supply / discharge the fluid into / from the cylinder portion 37 to operate the sub-extrusion pin 35 with respect to the extrusion pin 14. Adjust.

In the present invention, therefore, the movable block 27 can be shared as a fixing means for fixing the extra thickness portion 15. In this case, when the mold is opened after molding, first, the movable mold 2 is set in a semi-opened state in which it is slightly separated from the fixed mold 1. In this state, the movable block 27 is moved forward by the operation of the cylinder device 28, and the movable block 27 previously moves the movable block 27. The surplus portion 15 is pressed down, and subsequently the extrusion plate 33 is raised to extrude the molded body 11 by the extrusion pin 14. Then, since the surplus portion 15 is pressed by the movable block 27, a shearing force acts on the connecting portion between the molded body 11 and the position-fixed surplus portion 15, so that the surplus portion 15 is removed from the molded body 11. Divided. After the excess thickness portion 15 is divided, the movable die 2 is largely separated from the fixed die 1 to be in a completely open state, and at the same time, the extrusion plate 33 is further raised and the excess thickness portion 15 is moved by the auxiliary extrusion pin 35. Extruded. The movable block 27 may be provided in the movable die 2 instead of being provided in the fixed die 1 as in the above-described embodiment.

Further, according to the present invention, a fixing means for fixing the extra thickness portion 15 can be provided on the sub-extrusion pin 35. 6 to 8 show an embodiment thereof, in which a small-diameter locking portion 45 is provided at the tip end portion of the sub-extrusion pin 35, and an annular groove 46 is provided in the locking portion 45 as needed (see FIG. 7). ), Or a notch 47 that is inclined so that the depth increases toward the base end side (FIG. 8). In this case, the sub-extrusion pin 35
Cylinder part 37 (FIG. 4) of the two-step extrusion mechanism 36 supporting the
A spring for urging the base end large-diameter portion 38 of the sub-extrusion pin 35 always downward is disposed in this position. As a result, when the molten resin filled in the sub-cavity 23 is solidified and the surplus portion 15 is formed, the contraction causes the surplus portion 15 to stick to the locking portion 45. As a result, after molding as described above, When the molded body 11 is extruded by the push-out pin 14, the rise of the surplus portion 15 is restricted by the frictional resistance (pulling resistance) with the locking portion 45, and the surplus portion 15 is formed as in the above embodiment. Divided from 11. If the locking portion 45 is provided with the annular groove 46 or the notch 47 as described above, the pull-out resistance increases, and the division of the excess thickness portion 15 becomes more reliable. The locking portion 45 has, for example, a diameter d = 5 mm and a length l = 10.
The depth h of the annular groove 46 or the notch 47 is set to about 1 mm, respectively. In addition, the two-stage extrusion mechanism 36
When the above is configured as a fluid pressure cylinder as described above, the spring is of course unnecessary.

Further, the present invention can be applied to a hollow injection molding device having no work take-out device 41, movable block 27, or auxiliary extrusion pin. In this case, the fixing means for fixing the extra thickness portion 15 is a metal. It may be separately provided around the mold or inside the mold. In this case, FIGS.
It can also be applied to a mold having a sub-cavity 7 as shown in FIG.

[0033]

As described above in detail, according to the hollow injection molding apparatus according to the present invention, the surplus portion can be divided in the mold by utilizing the extrusion of the compact by the extrusion pin. In addition, a separate step of dividing the excess thickness portion is not required, and a large improvement in productivity and a reduction in manufacturing cost can be achieved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a main structure of a hollow injection molding device according to the present invention.

FIG. 2 is an enlarged cross-sectional view of part A in FIG.

FIG. 3 is a cross-sectional view showing a usage mode of the present hollow injection molding device.

FIG. 4 is an enlarged sectional view of a B part in FIG.

FIG. 5 is a cross-sectional view showing a usage mode of the hollow injection molding device.

FIG. 6 is a cross-sectional view showing an embodiment in which a fixing means is provided on the auxiliary extrusion pin.

FIG. 7 is a cross-sectional view showing an embodiment in which a fixing means is provided on a sub-extrusion pin.

FIG. 8 is a cross-sectional view showing an embodiment in which a fixing means is provided on the auxiliary extrusion pin.

FIG. 9 is a cross-sectional view showing a mold structure of a conventional hollow injection molding device.

FIG. 10 is a cross-sectional view showing a mold structure of a conventional hollow injection molding device.

FIG. 11 is a cross-sectional view showing a usage state of a conventional hollow injection molding device.

[Explanation of symbols]

 1 Fixed Type 2 Movable Type 3 Product Cavity 11 Molded Body 14 Extrusion Pin 15 Excess Part 22 Communication Passage 23 Sub Cavity 27 Movable Block 28 Movable Block Driving Cylinder Device 33 Extrusion Plate 35 Sub Extrusion Pin 36 Two-Step Extrusion Mechanism 45 Locking Part 46 Annular groove 47 Notch

Claims (4)

[Claims] 1. A mold provided with a sub-cavity in communication with a product cavity is provided with a movable block for varying the volume of the sub-cavity, and a pressurized fluid is injected into a molten resin injected into the product cavity. Then, in a hollow injection molding device in which a hollow portion is formed while a part of the molten resin is allowed to flow into the sub-cavity, and a molded body is extruded by an extrusion pin, the extrusion of the molded body by the extrusion pin is prevented. Then, the hollow injection molding apparatus is provided with a fixing means for fixing the excess thickness portion solidified in the sub-cavity. 2. The hollow injection molding apparatus according to claim 1, wherein the fixing means is provided in a work taking-out means for taking out a molded body from a mold. 3. The hollow injection molding apparatus according to claim 1, wherein the movable block is shared as the fixing means. 4. A sub-extrusion pin for extruding a surplus portion solidified by the sub-cavity, further comprising:
A locking means that is connected to the extrusion plate via a two-stage extrusion mechanism that operates the auxiliary extrusion pin with a time lag from the extrusion pin, and that the fixing means is provided at the tip of the auxiliary extrusion pin and that locks the extra thickness portion. The hollow injection molding apparatus according to claim 1, wherein the hollow injection molding apparatus is formed from a portion.