JPH0671731B2 - Method for manufacturing molded body with insert - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a molded product having an insert such as a buried nut.

[Prior Art] For example, as shown in FIG. 5, a resin molded body having an insert 102 such as an embedded nut in a boss 101 is known. As a method of manufacturing such a molded body, an insert molding method in which the insert and the molded body are integrally joined by arranging and molding the insert 102 in a molding die is generally used.

[Problems to be Solved by the Invention] By the way, in a resin-made molded product having an insert, the pull-out strength when attached to another component via the insert,
In order to increase the insert holding strength such as the rotation strength, it is effective to increase the wall thickness of the boss portion around the insert. However, when the thickness of the boss portion is increased, sink marks are generated on the surface of the molded body, which may impair the aesthetic appearance. In order to prevent such defects while maintaining high insert holding strength, the wall thickness of the general part of the molded body (hereinafter referred to as the general wall thickness) must be increased.
In this case, there is a problem that the weight of the molded body is increased and the material cost is increased.

The present invention has been made in view of such circumstances,
The object of the present invention is to achieve the trade-off between improving insert holding strength and preventing sink marks without increasing the general wall thickness of the molded body more than necessary.

[Means for Solving the Problems] A method of manufacturing a molded article having an insert according to the present invention is a method of forming a general thick portion and a plurality of thick boss portions locally formed in the general thick portion and holding the insert. A method for producing a molded body comprising: a plurality of large lumps forming a large part of a boss by arranging an insert in a preforming mold and molding; and a bridge portion connecting the plurality of large lumps to each other. The pre-forming step of forming a pre-formed body in which the insert is integrally joined to the large lump part and the boss that is integrally joined to the pre-formed body by arranging the pre-formed body in the main mold and performing molding. It is characterized in that the remaining part of the part and the main forming step of forming a general thick part are sequentially performed.

As the insert used in the present invention, conventionally used inserts such as nuts, bolts and pins can be used as they are.

The preforming step is a step of arranging the insert in a preforming die to form a preform. As a molding method, conventionally known molding methods such as injection molding, compression molding, transfer molding and the like can be used. The formed preform is then integrally joined to the insert.

The shape of the preform may be, for example, the shape of the boss portion. As a result, since the general wall thickness of the molded body can be made substantially uniform, the occurrence of sink marks can be prevented.

The main forming step is a step of forming the main formed body by disposing the obtained preformed body in the main forming die. That is, the preform body itself is used as an insert for molding. The molding method can be selected from the same molding methods as those in the preforming step. The same molding method as the preforming step may be used, or a different molding method may be used. As a result, a main compact integrally formed with the preform is formed.

The molding materials used in the preforming step and the main forming step may be the same or different. For example, if the same material or the same kind of material is used, the bonding strength between the preform and the main body can be made sufficiently high. It is also possible to form the preform from a soft material. In this way, the vibration or the like acting on the insert is buffered by the preform, so that it is possible to impart a vibration damping effect. A thermoplastic resin is generally used as the molding material, but a thermosetting resin can also be used. Also, not only resin,
It can also be applied to the molding of rubber materials or ceramic materials.

In the manufacturing method of the present invention, the preforming step and the main forming step may be performed separately, but the first cavity for forming the preform and the second cavity for forming the main body are formed in one mold. It is desirable to form the two types of cavities and simultaneously mold the preform and the main form. In this way, after opening the mold and taking out the main molded body, the first
The preform formed in the cavity is taken out and placed in the second cavity. Then, the mold is clamped and molded to mold the next main molded body and pre-molded body. In this way, since the main molded body and the preformed body can be molded at the same time, the production cycle is reliably synchronized, and there is no excess or deficiency in the number of preformed bodies. Further, the increase in man-hours can be suppressed to a minimum.

[Operation and Effect of the Invention] In the method for producing a molded article having an insert of the present invention, first, a preformed article having an insert is formed, and then the preformed article is arranged in a main forming die to form a main molded article. Can be formed.
Even if the preform has a sink mark, no problem will occur unless the main body is abnormal. Therefore, the wall thickness of the preform can be increased, and the insert holding strength can be increased even with only the preform. As a result, it is not necessary to provide a thick portion such as a boss portion in the formed body, and the general thickness can be made uniform, so that sink marks are prevented from occurring on the surface of the formed body. In addition, since the general wall thickness of the molded body can be minimized, increase in weight and material cost can be prevented.

That is, according to the manufacturing method of the present invention, sink marks are prevented from being generated on the surface of the molded body. Since the wall thickness around the insert can be made sufficiently thick, the insert holding strength such as pull-out strength can be increased. Furthermore, even if the insert and the main molded body have low bond strength, by selecting a material with a high bond strength between the insert and the main molded body for the pre-molded body, the insert can be made stronger in the main molded body. Can be held. Therefore, the degree of freedom in selecting the material of the insert and the molded body is improved.

Further, in the manufacturing method of the present invention, the preform has a shape in which a plurality of large lump portions forming the majority of the boss portion are connected to each other by a bridge portion. Therefore, since a plurality of inserts are held in one preform, the placement work and the positioning work in the main mold are extremely easy and the productivity is high.

[Examples] Hereinafter, specific examples will be described. This embodiment applies the present invention to the manufacture of a bumper for a water scooter. In a water scooter, water bumps into the bumper during traveling on the water, so that the mounting structure between the bumper and the main body needs to be strong. Therefore, a plurality of nuts are embedded in the bumper, and the scooter body is firmly connected with the bolts.

(Example 1) Two steel nuts (hereinafter referred to as inserts) having an outer diameter of 8 mm were arranged in a preforming die, and a preform was formed by injection molding using polypropylene resin. A perspective view of the preform 1 is shown in FIG. The preform 1 is composed of two large lump portions 10 holding the insert 2 and a bridge portion 11 connecting the large lump portions 10 in a bridge shape. The large lump portion 10 has a thickness of 4 mm and covers the outer peripheral surface of the insert 2.

Next, the preform 1 is placed in the main body, and the main body is formed by injection molding using the same polypropylene resin as described above. Furthermore, the obtained main molded body is placed in another mold and injection-molded using a thermoplastic elastomer (trade name "Lavalon", manufactured by Mitsubishi Petrochemical Co., Ltd.) to give a soft surface to the main molded body. A bumper having a skin layer of

The perspective view of the main part of the obtained bumper 3 is shown in FIG.
A sectional view taken along line A is shown in FIG. The bumper 3 is composed of a main molded body 30 made of polypropylene and a skin layer 31 covering the surface of the main molded body 30, and is a large block in a cylindrical holding portion 32 protruding to the back side of the main molded body 30. The portion 10 is integrally embedded to form a boss portion. And insert 2 from the boss
The insert 2 is integrally connected to the preform 1. Therefore, the insert 2 is integrally bonded and held in the main molded body 30.

In the obtained bumper 3, the general wall thickness of the molded body 30 is 3 m.
It is uniform in m and no sink mark is generated on the surface of the molded body 30. As a result, the bumper 3 has an excellent appearance on the surface of the skin layer 31. It is known that when a shrinkage occurs in the molded body, a sinkage also occurs in the skin layer. Further, since the insert 2 is held by the total thickness of the cylindrical portion 10 of the preform 1 and the holding portion 32 of the main body 30, the insert 2 has a high drawing strength.

(Example 2) This example is the same as Example 1 except that the preform 1 and the main body 30 were molded using the mold having the structure shown in FIG.

The molding die 4 used is the first for molding the preform 1.
It has a cavity 41 and a second cavity 42 for molding the main molded body, and each cavity has the same runner.
It communicates with 40.

Molding was carried out as follows using this molding die. First, the insert 2 is placed in the first cavity 41, and polypropylene resin is injection-molded from the runner 40. The injected resin fills the inside of the first cavity 41 and the second cavity 42 from the runner 40, and the preform 1 is molded. Then open the mold. Since there is no preform 1 in the second cavity 42 at the time of the first molding, the molding formed in the first cavity 2 of the first cavity is discarded. Then, the second preliminarily molded body 1 molded in the first cavity 41 is emptied
Empty first cavity 41 placed in cavity 42
The insert 2 is arranged in the mold, and polypropylene resin is injection-molded again after the mold is clamped. At this time, the preformed body 1 is molded in the first cavity 41, and the main molded body 30 is molded in the second cavity 42. Then, the mold is opened, the main molded body 30 is taken out, and the same work is repeated to perform molding one after another.

That is, if the forming die as in this embodiment is used for forming, the preform 1 and the main body 30 can be formed at the same time, so that the increase in the number of steps can be suppressed to a minimum. In addition, there is no excess or deficiency in the number of preforms, and efficient production is possible.

[Brief description of drawings]

1 to 3 relate to a method for manufacturing a molded body having an insert according to an embodiment of the present invention, FIG. 1 is a perspective view of a pre-molded body, FIG. 2 is a perspective view of a main part of a manufactured bumper, FIG. 3 is a sectional view taken along the line AA of FIG. FIG. 4 is a schematic sectional view of a molding die used in another embodiment of the present invention. FIG. 5 is a sectional view of a molded body having an insert formed by a conventional manufacturing method. 1 ... Preform, 2 ... Insert 3 ... Bumper, 4 ... Mold 10 ... Large part, 11 ... Bridge part 30 ... Main body, 31 ... Skin layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-56-55237 (JP, A) JP-A-59-48133 (JP, A) JP-A-52-10357 (JP, A) JP-A-60- 18319 (JP, A) JP 59-73930 (JP, A)

Claims (1)

[Claims] 1. A method of manufacturing a molded body comprising a general thick portion and a plurality of thick boss portions which are locally formed in the general thick portion and hold an insert, wherein the insert is preformed. The insert is integrally formed in the large lump portion, which is composed of a plurality of large lump portions forming a large part of the boss portion and a bridge portion connecting the plurality of large lump portions to each other. A preforming step of forming a combined preformed body, and a remaining portion of the boss portion and the general wall thickness integrally combined with the preformed body by arranging and molding the preformed body in a main mold. A method for manufacturing a molded article having an insert, which comprises sequentially performing a main molding step of forming a part and a step.