JP2000355021A - Insert mold molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To meet the height accuracy of a part to be insert-molded by making a force to be generated by the pressure of a fluid act upon a platelike member so that the platelike member is deformed in a specified direction in a mold. SOLUTION: A fixed side core pin 12 is made to slide within a range defined by its enlarged diameter, in a hole 13 for a stopper formed on a fixed side cavity 11 and the upper end 12a of the core pin 12 has the end face receiving the pressure of a molten resin injected into a runner 14 to generate a downward force, which in turn, is conveyed to the center pole 1a of a yoke 1 from the lower end 12. Further, a part is insert-molded by retaining the center pole 1a in a mold in such a state that the pole 1a is forcibly deformed so that the tip of the pole 1a comes to a specified position. Thus it is possible to meet the height accuracy of the part to be insert-molded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an insert molding method. More particularly, the present invention relates to a molding method for improving the dimensional accuracy between a member to be inserted and a resin structure to be molded in insert molding.

First, as an example of the background of the present invention, an example of the entire structure of an electromagnetic buzzer, which is a product including a buzzer case to which the molding method of the present invention is applied as a part, will be described. FIG. 3A is a plan view of the electromagnetic buzzer with the diaphragm removed, and FIG.
It is A sectional drawing. Reference numeral 1 denotes a yoke, which is made of a soft magnetic material having a high magnetic permeability such as permalloy, and has a central portion of a flat main body and a convex columnar center pole 1a integrated therewith. 2
Is a buzzer case, and the yoke 1 is molded with a resin in which the yoke 1 is inserted. The resin portion holds a peripheral portion of the yoke 1 and forms a cylindrical wall concentrically surrounding the center pole 1a.

Further, two lead frames 3 are insert-molded together with the yoke 1 in a part of the buzzer case 2. Both ends of a winding of a drive coil 4 wound in a flat cylindrical ring shape and fitted to a center pole 1a are connected to the exposed portion 3a therein. Reference numeral 5 denotes a permanent magnet, which contains a rare earth element, has a ring shape (partly cut away except for the molded part of the lead frame 1), is arranged around the drive coil 4, and is magnetized in the thickness direction. Reference numeral 6 denotes a vibration plate, which is a thin plate made of a soft magnetic material.
a and is attracted by the permanent magnet 5 and positioned.

A predetermined gap g is provided between the lower surface of the diaphragm 6 and the top of the center pole 1a. Drive coil 4
The voice current flowing through the diaphragm 6 changes the amount of magnetic flux connecting the center pole 1a and the center of the diaphragm 6, that is, the attractive force downward of the diaphragm 6, and generates sound. Therefore, the size of the gap g determines the amount of basic magnetic flux, the sensitivity of the diaphragm amplitude to the drive current, the degree of non-linearity of the attractive force, or limits the maximum amplitude of the diaphragm. It is an extremely important quantity for product quality control because it has a sensitive effect on characteristics.

2. Description of the Related Art As is apparent from FIG. 3B, a gap g is formed at the top (tip) of a center pole 1a of a yoke 1.
And the cylindrical top 2 of the buzzer case 2 on which the diaphragm 6 is placed
It is practically determined by the height difference from a. This difference in height is caused by the insert molding method of the buzzer case.

FIG. 4 is a sectional view of a main part showing a structure of a conventional mold for explaining a method of forming a buzzer case. Reference numeral 10 denotes a movable-side cavity (lower mold) into which a yoke 1 is inserted prior to resin molding, and a movable-side insert 1 is inserted into a main body.
0a is press-fitted, and a cavity 20 is formed to allow the injected resin to flow into the buzzer case. The movable insert 10a is provided with an escape hole 10b into which the center pole 1a of the yoke is inserted, and almost the entire upper surface thereof is a yoke pressing portion 10c.

Reference numeral 11 denotes a fixed-side cavity (upper die), the center of which has a yoke holding portion 11a for holding the yoke 1 in a large area during molding, and a movable-side yoke holding portion 10c.
At the same time, the yoke 1 during insert molding is held in a large area. Although gates and runners as resin flow paths are also provided, these are not shown. In addition, the lead frame is also insert-molded together with the yoke, but the portion relating to the lead frame is not shown because it does not directly relate to the problems dealt with in the present invention.

[0007]

In the description of FIG. 3B, it has been stated that the value of the gap g is important for the acoustic characteristics of the buzzer. As shown in the figure, the gap g is formed between the top of the center pole 1a and the top 2a of the buzzer case 2 (the lower end of the cylindrical cavity 20 in FIG.
Is almost determined by the difference between the height and the height. The position of the cavity bottom 20a in FIG. 4 is common to all products depending on the mold. However, as shown in FIGS. 2A and 2B, the height from the bottom surface of the yoke to the tip of the center pole 1a, that is, the thickness H of the projection may vary depending on the manufacturing method of the yoke 1. However, the individual plate thickness of the yoke is assumed to be sufficiently accurate), in which case the size of the gap g is not stable.

There are various methods for processing the center pole of the yoke, such as header processing, joining of two parts (plate and cylinder), drawing from a plate material, and the like, but each has advantages and disadvantages. May be difficult to get out. When a yoke made by a processing method having such disadvantages is insert-molded by a conventional method, the value of the air gap g varies considerably, which causes unstable acoustic characteristics of an electromagnetic buzzer as a final product. There is a problem.

It is an object of the present invention to provide a semiconductor device having a projecting portion from a plate-like member and having an uneven height due to unevenness in the height of a part to be insert-molded, for example, a center pole portion of a yoke. An object of the present invention is to provide an insert molding method capable of satisfying precision of relative height with a molded synthetic resin member.

[0010]

Means for Solving the Problems In order to achieve the above object, in the insert molding method of the present invention, the following features (1), or a combination of (1) and (2), or ( It has features combining (2) and (3).

(1) In a molding method in which a plate-like member is insert-molded to form a resin structure on a part of the plate-like member, a part of the plate-like member forms the structure during insert molding. A gap-like space that allows the plate-shaped member to be slightly deformed is held in a portion of the mold other than the sandwiched portion and the cavity by the mold having a cavity portion. The mold is provided so as to face the plate-like member, and the mold further includes means for applying a force by a fluid pressure to the plate-like member to deform the plate-like member in a predetermined direction.

(2) The plate-like member has a convex portion at a substantially central portion, and the resin structure is formed at a peripheral portion of the plate-like member away from the convex portion, and the front surface of the convex portion and The back surface is sandwiched between two components in the mold, that is, a component fixed to the mold, and a component slidable inside the mold, and fixed to the mold. The component member abuts on one surface of the convex portion, and the component member slidable inside the mold has one end abutting on the other surface of the convex portion and the other end exposed in the runner and injected. Receiving the pressure of the molten resin and transmitting the force to the other surface of the projection.

(3) The plate-like member is a yoke of an electromagnetic buzzer, the projection is a center pole of the yoke, and the resin structure is a diaphragm that faces the center pole via a gap. The buzzer case must be held.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view of a main part of a mold used in the present invention. Parts common to the conventional molds are denoted by the same symbols as in FIG. 4 and will not be described again. FIG.
The difference in structure from the conventional mold is that the yoke pressing portions 10c and 11a sandwich the yoke 1 only at its peripheral edge, and the plate-like portion inside the peripheral edge does not touch the mold. The gaps 10e and 11b are provided so that bending deformation can be performed, and the movable side insert 1 of the movable mold cavity 10 is provided.
0a has a movable core pin 10d which comes into contact with the tip of the center pole 1a of the yoke 1 at the time of insert molding, and the fixed core pin 1 is inserted into the fixed cavity 11 which moves integrally with the fixed cavity spacer 13.
2 is fitted so as to be slightly slidable in the vertical direction,
“a” communicates with the resin runner 14, and the lower end 12 c pushes behind the center pole 1 a.

Next, the operation at the time of injection molding will be described. The movable-side core pin 10d is press-fitted into the movable-side insert 10a, and the upper end position thereof is adjusted to a position where the gap g is correctly set to a desired dimension (when the product is obtained), and then the movable-type cavity 10 is moved. Fix in advance. The fixed-side core pin 12 can slide within a limited range because of the large-diameter portion 12b in the stopper hole 13 provided in the fixed-side cavity 11, but the end face of the upper end 12a has the molten end face injected into the runner 14. Under the pressure of the resin (approximately 40 kg per square cm, which is sufficiently high), a downward force is generated, and the force is generated at the lower end 12 c
To the center pole 1a of the yoke 1.

The lower end of the center pole 1a is strongly pressed against the movable core pin 10d by the force generated by the injected resin, and is held at a specified position. Therefore, even if the thickness H of the center pole 1a varies, the difference in height from the cavity bottom 20a, that is, the gap g of the product, is kept constant without change. At this time, a portion of the intermediate band between the fixedly held peripheral portion of the yoke 1 and the center pole 1a elastically restricted in position is formed as a shallow concave portion on the movable side cavity 10 side and the fixed side cavity 11 side, respectively. Since the gap 10e and the gap 11b are provided, it can be freely bent and deformed.

As described above, the yoke 1 has the center pole 1a.
Irrespective of the difference in the thickness H of the portion, the center pole 1a is insert-molded while being held in a mold in a state where it is forcibly deformed so that the tip of the center pole 1a comes to a fixed position. The value of the value g is automatically corrected, and even if there is a difference in the thickness H of the convex portion, the variation of the value g can easily be kept within an allowable range. Even if the yoke 1 is slightly warped, the movable side core pin 10 d
, The dimensional accuracy of the gap g of the product after molding can be improved.

Although an example of the embodiment of the insert molding method of the present invention has been described above, the present invention is not limited to this embodiment and can be implemented with various modifications. For example, as a method of applying force to the convex part during molding, instead of applying the pressure of the molten resin to the end of the fixed-side core pin, different types of fluid such as air pressure and hydraulic pressure introduced from outside the mold to the fixed-side core pin It is conceivable to apply a force by pressure. Further, such a fluid pressure may be received by another member inside and outside the mold, and the force generated by the member may be relayed to the fixed core pin (or its equivalent) and transmitted.

Further, the present invention can be applied to a case where a plate-like portion (for example, a yoke main body) or a convex portion (for example, a center pole) of a plate-like member has a complicated shape. The portion where the resin structure is formed is not limited to the peripheral portion of the plate member.
The object of the present invention is not limited to the electromagnetic buzzer.

[0020]

According to the present invention, since insert molding is performed while restricting the projecting portion from the plate member to a specified position by using a mold, the dimension between the projecting portion and the resin-molded portion can be accurately determined. Can be aligned well. In addition, since the thickness of the protruding portion is allowed to vary, the method of manufacturing the plate member is not limited, and the degree of freedom in product design can be increased. Even if the plate-like member is warped, it can be formed while correcting the warp. The yield can be increased by setting the allowable dimensional tolerance of the plate-shaped member as a component to be larger than before. Moreover, the additional processing required for the mold is small, and the processing cost is hardly increased.

Further, when the present invention is applied to an audio device such as a buzzer, the gap size between the diaphragm and the center pole can be made uniform, and there is an effect that a product with less variation in acoustic characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a mold used in the present invention.

FIGS. 2 (a) and 2 (b) are side views of a yoke of an electromagnetic buzzer which is a component to be subjected to the molding method of the present invention.

FIG. 3A is a plan view of an electromagnetic buzzer with a diaphragm removed, and FIG. 3B is a cross-sectional view of the electromagnetic buzzer taken along line AA.

FIG. 4 is a sectional view of a main part showing a structure of a mold in a conventional molding method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Yoke 1a Center pole 2 Buzzer case 2a Cylindrical top part 3 Lead frame 3a Exposed part 4 Drive coil 5 Permanent magnet 6 Diaphragm 10 Movable cavity 10a Movable insert 10b Escape hole 10c Yoke holding part 10d Movable core pin 10e Gap 11 Fixed side cavity 11a Yoke holding part 11b Clearance 11c Stopper hole 12 Fixed side core pin 12a Upper end 12b Large diameter part 12c Lower end 13 Fixed side cavity spacer 14 Runner 20 Cavity 20a Cavity bottom g Gap H Convex part thickness

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Claims (3)

[Claims] In a molding method for insert-molding a plate-like member to form a resin structure on a part of the plate-like member, a part of the plate-like member forms the structure during insert molding. A gap-shaped space that allows the plate-shaped member to be slightly deformed is held between the held portion and the portion of the mold other than the hollow portion. The mold is further provided with means for applying a force by the pressure of fluid to the plate-shaped member to deform the plate-shaped member in a predetermined direction. Insert molding method. 2. The plate-like member has a convex portion at a substantially central portion, and the resin structure is formed on a peripheral portion of the plate-like member away from the convex portion, and a front surface and a rear surface of the convex portion are provided. Is sandwiched between two components in the mold, that is, a component fixed to the mold, and a component slidable in the mold, and fixed to the mold. The component member abuts one surface of the convex portion, and the component member slidable inside the mold has one end abutting the other surface of the convex portion, and the other end is exposed and injected into the runner. 2. The insert molding method according to claim 1, wherein the force is transmitted to the other surface of the projection by receiving the pressure of the molten resin. 3. The plate-shaped member is a yoke of an electromagnetic buzzer, the projection is a center pole of the yoke, and the resin structure holds a diaphragm facing the center pole via a gap. 3. The method according to claim 2, wherein the buzzer case is a buzzer case.