JP2861468B2 - Insert molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insert molding method when an insert part has a groove such as a screw groove.

[0002]

2. Description of the Related Art In recent years, insert molding of insert parts having a thread groove or the like, such as a rotor portion of a stepping motor, has been increasing. However, in the case of insert molding with such a part, resin leakage from the groove occurs. Therefore, a partially cut-type insert part without a groove is used in the insert part with the resin.

Hereinafter, a conventional insert molding method will be described with reference to FIG. FIG. 3 shows a cavity portion of a molding die of a plastic magnet of a rotor portion for a stepping motor, where 11 is an upper mold portion, 12 is a lower mold portion, 13 is a sprue gate portion, and 14 is an insert part having no groove in the insert portion. , 15 is a plastic magnet resin portion, 16 is a core, and the core 16 holds a part of the thread groove portion 14a of the insert component 14 and a part 14b where the thread groove is not formed. It will be formed on the outer periphery of the part that is not formed.

[0004]

With respect to the above-mentioned conventional insert part 14, a partly threaded screw shaft having no groove formed in the insert part with the plastic magnet resin part 15 is formed by a fully threaded type by rolling. Is cheaper by 20 to 30%, and as a result, resin leakage does not occur, but it is disadvantageous in cost.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an insert molding method which eliminates the above-mentioned conventional drawbacks and does not cause resin leakage from a groove even in an insert part such as a full screw type screw shaft.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is to provide an insert part having a groove over its entire length on an upper end surface of a core holding the insert part in a cavity of a molding die, and along the insert part. In this method, a projecting small diameter projection is provided, and a resin material is injection-molded in the cavity.

[0007]

According to this method, during injection molding, resin leakage from the groove of the insert part can be suppressed inside the product, and defects in the function of the part due to resin leakage outside the product can be eliminated.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment in molding a plastic magnet for a rotor for a stepping motor. FIG. 1 shows only the vicinity of the cavity portion of the molding die, where 1 is an upper die portion, and 2 is a lower die portion, and these constitute a molding die. 3 is a sprue gate portion provided on the upper mold portion 1, 4 is an insert part of a type having a thread groove formed over its entire length, 5 is a plastic magnet resin portion,
Reference numeral 6 denotes a core, which is disposed in the cavity of the molding die and holds the lower part of the insert part 4, and a projection 7 projecting upward along the insert part 4 is provided on the upper end surface.

The insert molding method using the molding die configured as described above will be described.

First, a resin injected from a molding die machine is filled into a plastic magnet resin portion 5 which is a molding cavity from a sprue gate portion 3. At this time, the resin naturally leaks from the screw groove 4a of the insert part 4 in which the screw groove 4a is formed over the entire length. Therefore, as shown in the figure, the core 6 is provided with a projection 7 (portion t in the height direction) that penetrates into the lower surface of the plastic magnet resin portion 15 so that the resin leakage from the screw groove 4a is limited to the range of this t portion. The resin is prevented from leaking out from the protrusion 5a of the plastic magnet resin portion 5 formed outside the protrusion 7 inside.

The outline of the present embodiment will be described below. Outline of molding Mold structure: 3 plates, pinpoint gate molding Material: Plastic magnet resin (Fe particles + 1)
2 nylon) Insert parts: All threaded products by rolling (φ3, L =
45 mm, pitch p = 1.0 to 3.0) Mold temperature: 60 ° C. Resin temperature: 300 ° C. t-dimension (projection 7 of core 6): 3.5 mm Injection pressure: 700 to 1000 kg / cm ² In the example, the groove 4 of the insert part 4
Although a is a thread groove, as shown in FIG. 2, even for an insert part 4 having a linear groove 4b in the longitudinal direction,
The above method is effective and can be applied to all insert molding in which resin leakage is considered to occur from the groove of the insert part 4 by insert molding.

[0012]

As described above, according to the present invention, it is possible to inexpensively prevent resin leakage to the outside of a product for a grooved insert part. Insert molding of a whole rolled screw, which is less expensive than an insert part having a thread groove, is also possible, which can greatly contribute to cost reduction of the product itself.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a cavity of a molding die in an insert molding method of the present invention.

FIG. 2 is a front view of the insert part on the other side.

FIG. 3 is a sectional view of a cavity of a molding die showing a conventional insert method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Upper mold part 2 Lower mold part 3 Sprue gate part 4 Insert part 4a Screw groove 5 Plastic magnet resin part 6 Core 7 Projection

Claims (1)

(57) [Claims] A small-diameter projection protruding upward along the insert component is provided on an upper end surface of a core for holding an insert component having a groove over the entire length in a cavity of a molding die, and a resin material is filled in the cavity. Insert molding method for injection molding.