JPS63221020A - Preparation of molded item having undercut - Google Patents

Abstract

PURPOSE:To make it possible to mold a required shape on the surface, by closing a mold where an undercut is formed with a bag-like freely expandable and contractable member, acting a fluid pressure in the expandable and contractable member, removing the fluid pressure after molding, contracting and peeling off the expandable and contractable member, and thereafter opening the mold. CONSTITUTION:A cavity 3 and a core are opened and a pressurized fluid is sent in an expandable and contractable member 5 from a tube 8. The pressure is made higher than the pressure of the resin when being molded. In this condition, according to the usual blow molding operation, a parison is placed between the cavity 3 and a core 4, which are then closed. The parison is expanded by sending a compressed air and is contacted under pressure with the inner face of the mold. At this time, the expandable and contractable member 5 acts as a part of the core of the mold and an undercut part 3 is formed on a molded item 1 in accordance with the shape of the expandable and contractable member 5. Then, the pressurized fluid in the expandable and contractable member 5 is sucked by means of the tube 8. The expandable and contractable member 5 is thereby peeled off from the undercut part 2 of the molded item 1 and the cavity 3 and the core 4 are opened to take out the molded item 1.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing a molded product when the molded product has an undercut during injection molding, blow molding, etc. of synthetic resin.

Conventional technology An undercut is a convex part or a concave part in a direction that intersects the drawing direction of a molded product with respect to the mold, and in a molded product having such an undercut, the molded product and the mold will not mesh with each other as it is. It cannot be removed from the mold.

Therefore, conventionally, when molding a molded product having such an undercut, the undercut part is molded using means such as an angular pin, dogleg cam, rack and pinion, etc. in the drawing direction. It gave a movement in the direction that crosses the object.

Problems to be Solved by the Invention However, in these methods, the mold must be formed of a plurality of blocks, and each of these blocks must be given separate movement, and the movement of these blocks must be Since this is usually controlled only by the movement of the mold in the opening direction, the structure of the mold is extremely complex and large. Especially when there is an undercut on the core side, such as with a female thread, the block must make all the necessary movements within an extremely narrow space, making it extremely difficult to design the mold. be.

Moreover, since the blocks that make up the mold slide against each other each time the mold is opened and closed, it is necessary to ensure lubrication at all times. If the lubricity decreases during molding, the sliding parts will wear out and seize, resulting in molding. The mold is often damaged. Furthermore, thermal expansion of the mold due to the heat generated during molding may cause errors in the assembly of each block, making it difficult to slide or conversely causing play between the blocks.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method for manufacturing a molded product having an undercut in an extremely simple manner.

As a means for solving the problems, the present invention forms an undercut portion of a mold with a bag-like elastic member, applies fluid pressure to the elastic member in a closed state of the mold, and forming a molded article on a surface of a member, then removing fluid pressure within the telescoping member, contracting the telescoping member to separate the telescoping member from the molding, and then opening the mold. This is a characteristic feature.

FIG. 1 shows a method of manufacturing a molded product having an undercut by a blow molding method to which the present invention is applied.

The molded product 1 molded by this method is a hollow article in the shape of a substantially boat as shown in FIG. 2, and an undercut portion 2 that digs inward is formed inside one end thereof.

In FIG. 1, 3 and 4 are the cavity and core of the mold, and the cavity 3 has a molding surface that fits the side and bottom surfaces of the molded product 1, and the core 4 has a It has a molding surface that matches the inner surface of the molded product 1 except for the undercut portion 2.

Reference numeral 5 denotes an elastic member attached to the core 4, which is made of a woven fabric made of heat-resistant, high-strength, low-elongation fibers such as aramid fibers, glass fibers, metal fibers, carbon fibers, etc. It is sewn into a bag shape that matches the undercut portion 2 of the molded product 1, and an airtight layer made of a rubber-like elastic material is formed on at least the inner surface of the bag, and an anti-adhesion treatment using fluororesin or the like is applied to the outer surface. There is.

Then, this elastic member 5 is fitted into the through hole 6 formed in the core 4, and its tip is placed at a position that fits the undercut portion 2 of the molded product 1 on the molding surface, and the opening is connected to the flange fitting. 7 to fix it to the core 4. Also, the flange fitting 7
A pipe 8 is attached to the pipe 8, and the chain pipe 8 opens into the telescopic member 5.

Next, the operation of molding the molded product 1 according to the present invention using this mold will be explained. First, with the cavity 3 and core 4 open, pressurized fluid is introduced into the expandable member 5 from the pipe 8 to apply fluid pressure to the expandable member 5. Although air, water, oil, etc. can be used as this pressure fluid, it is preferable to use a liquid whose volume does not change due to pressure. In addition, the pressure of the pressure fluid needs to be higher than the pressure of the resin during molding, and in the case of blow molding, the air pressure blown during molding is about 5 to 6 ksIi, so it is necessary to The degree is appropriate.

In this state, the parison is placed between the cavity 3 and the core 4 according to normal blow molding operations, the cavity 3 and the core 4 are closed to compress the parison, and compressed air is sent into the parison. The parison is inflated and pressed against the inner surface of the mold. At this time, the elastic member 5 is
Acting as part of the core of the mold, the molded product 1 is pressed against the surface of the elastic member 5, and an undercut portion 2 is formed according to the shape of the elastic member 5. This state is shown by the solid line in FIG.

Next, the pressure fluid inside the telescopic member 5 is sucked through the pipe 8, and negative pressure is applied within the telescopic member 5. As a result, the expandable member 5 reduces its volume and contracts as shown by the chain line in FIG. 1, and is separated from the undercut portion 2 of the molded product 1, thereby dissolving the interlocking relationship between the molded product 1 and the mold. By opening the cavity 3 and core 4 in this state, the molded product 1 can be removed from the core 4.

Note that when opening the mold, it is preferable to apply negative pressure to the telescopic member 5 as described above to actively contract the telescopic member 5, but depending on the shape and structure of the mold, the telescopic member 5 may simply be It is sufficient to simply remove the fluid pressure inside, and the elastic member 5 can escape from the undercut portion of the molded product 1 while being deformed.

Effects of the Invention According to the present invention, the expandable member 5 forming a part of the core 4 can be expanded and contracted by fluid pressure, so when molding the molded product 1, fluid pressure is not applied to the inside. The mold can be inflated and molded into a desired shape on the surface thereof, and the elastic member 5 can be deformed by removing the fluid pressure inside the elastic member 5 to escape from the undercut. can be opened. Therefore, the structure of the mold can be made simple, and there is no need to make each part of the mold make complicated movements in order to pull out the mold, and it is possible to form an undercut very easily and inexpensively with a small mold. Molded products can be molded.

Embodiments The method of the present invention is not only applicable to blow molding as described above, but also to other molding methods such as injection molding, transfer molding, and pour molding. However, in injection molding and transfer molding, the resin pressure is extremely high, approximately 100%
Since there may be as many as three layers in the pressure, the material and structure of the expandable member 5 must also be able to withstand this pressure.

Further, in the example shown in FIG. 1, the bent elastic member 5 constitutes a part of the core 4 that molds the undercut portion 2 of the directly molded product 1, but the present invention is not limited to this. do not have. As shown in FIG. 3, a protrusion 9 is made to protrude from a part of the elastic member 5, and the elastic member 5 is fitted into a recess 10 not formed in the core 4, so that only the tip of the protrusion 9 is inserted into the molded surface of the core 4. It can also be made to protrude from the

Especially in injection molding using hard synthetic resin,
Even a minute recess of about 0.5 to 1 mm results in an undercut that cannot be removed from the mold, and in many cases it is necessary to use a complicated mold as described above to remove it. By employing the method shown in FIG. 3 when forming such minute recesses, it is possible to apply ultra-high fluid pressure exceeding the injection pressure within the expandable member 5 without giving much consideration to the withstand pressure of the expandable member 5. In addition, even if the elastic member 5 is thick, by removing the fluid pressure, the protrusion 9 can be retreated to the extent that it can escape from the undercut portion of the above-mentioned height, and the mold can be easily removed. .

Furthermore, it goes without saying that the present invention is not limited to application to the core 4 of a mold, but can also be applied to the cavity 3.

[Brief explanation of the drawing]

FIG. 1 is a central vertical cross-sectional view showing a state in which a molded product is molded by the blow molding method according to the present invention, and FIG. 2 is a perspective view of the molded product molded by the method. FIG. 3 is a central vertical sectional view showing an embodiment of the present invention. 1... Molded product 2... Undercut portion 3... Cavity 4...
・・Core 5・・・・Extensible member: 50 zu

Claims (1)

[Claims] 1 Forming an undercut part of the mold (3, 4) with a bag-shaped telescopic member (5), and applying fluid pressure within the telescopic member (5) when the mold (3, 4) is closed. The surface of the elastic member (5) is used as part of the mold to form a molded product (
1), after which the fluid pressure in the elastic member (5) is removed and the elastic member (5) is contracted to form the elastic member (5).
5) is peeled from the undercut portion (2) of the molded product (1), and then the molds (3, 4) are opened.