JP2000354298A - Manufacture of yoke for electromagnetic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower a working cost, to provide sufficient product accuracy and to reduce the problems of residual distortion as well by using a powder injection molding method for the manufacture of a yoke. SOLUTION: As a raw material, the powder of permalloy (weight ratio is about 8) and the powder of polystyrene (weight ratio is about 2) are mixed and kneaded well (process 1). An injection molding machine is provided, the mixture of the raw material is fused, supplied to an injection molding die, filled in a cavity having the shape of a product and then cooled in the molding die to harden the resin (process 2). A hardened product is taken out from the die (process 3) and heated inside a drying furnace and the resin component is vaporized and removed (process 4). A semiprocessed product in which metal particles are coarsely connected is sintered under a temperature near the melting point of a metal material and an end product provided with a prescribed dense composition is obtained (process 5). Though the semiprocessed product is slightly shrunk in the process of sintering, the shrinking rate is decided by a working condition and deformation is small. These conditions are sufficiently studied before mass production.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electromagnetic device, for example, a yoke used for an electromagnetic sounding body.

First, as a technical background, an example of an overall structure of an electromagnetic sounding body which is a product example to which the molding method of the present invention is applied will be described. FIG. 2 is a sectional view including the central axis of the electromagnetic buzzer. A main part of each component has a concentric circular structure except for a terminal lead frame and a cutout for accommodating the terminal lead frame, so that the structure can be easily understood even if the entire plan view is omitted. 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. Reference numeral 2 denotes a buzzer case, which is molded from a resin with the yoke 1 inserted therein. The resin portion holds a peripheral portion of the yoke 1 and forms a cylindrical wall surrounding the center pole 1a.

[0003] Two lead frames 3 are insert-molded together with the yoke 1 in a part of the buzzer case 2. Both ends of the winding of the drive coil 4 which is wound in a flat cylindrical ring shape and fitted to the center pole 1a are connected to the inner exposed portion 3a. 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 circular diaphragm, which is a thin plate made of a soft magnetic material, is placed on the cylindrical top 2a of the buzzer case 2, and is attracted and positioned by the permanent magnet 5.

A predetermined gap G is provided between the lower surface of diaphragm 6 and the top of 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 sensitivity of the diaphragm amplitude to the basic amount of magnetic flux and the drive current, the attractive force and the degree of its nonlinearity, or limits the maximum amplitude of the diaphragm. It is an extremely important quantity for quality control of products because it has a sensitive effect on acoustic characteristics.

FIG. 3 shows the shape of the yoke 1. (A) is a plan view, and (b) is a cross-sectional view passing through a central axis. The error in the height H of the center pole 1a, the thickness T of the flat plate portion 1b, and the amount of warpage B of the flat plate portion 1b are component dimensions that directly affect the value of the gap G in the completed product in FIG. Therefore, in producing a yoke as a part, it is necessary to adopt a manufacturing method that sufficiently satisfies the shape accuracy of a part mainly including the parts, not to mention the cost reduction.

[0006]

2. Description of the Related Art A main method of manufacturing a yoke which has been conventionally used will be examined. (1) Header processing method: At a normal or high temperature, the tip of a rod-shaped or cylindrical material is hit with a mold to form a shape including a center pole portion. Although the manufacturing cost is low, there is a problem that it is difficult to obtain the dimensional accuracy of the finished part, and the gap G is likely to vary.

(2) Press-in assembly method: A center pole portion processed by an automatic lathe is press-fitted into a center hole of a flat plate portion subjected to press punching. Since one part is divided into two parts and processed and further assembled, the cost is high, and the assembling accuracy also affects the dimensional accuracy of the finished product. As the yoke material, permalloy, which is a high magnetic permeability material, is desirable. However, this material is soft and rich in ductility, and is not very suitable for the processing methods (1) and (2).

(3) Drawing method: A strip-shaped plate material is subjected to several stages of processing in small amounts by a progressive die to gradually form a projection serving as a center pole by drawing at the center of the plate material. Perform sampling. The processing method itself is suitable for a permalloy material, but if the residual strain is not removed by annealing, the magnetic properties deteriorate, which makes it difficult to reduce the size and weight, and the progressive type is expensive.

[0009]

Electromagnetic devices such as electromagnetic sounding bodies are in great demand, especially in portable electronic equipment, and their applications are expanding. Therefore, a new processing method which improves the drawbacks of the prior art is required. SUMMARY OF THE INVENTION An object of the present invention is to provide a new method for manufacturing a yoke, which has a low processing cost, provides sufficient product accuracy, and has little problem of residual distortion.

[0010]

According to the above object, a method of manufacturing a yoke according to the present invention has the following features. (1) a step of forming a powder material in which a magnetic material powder having a high magnetic permeability and a synthetic resin material powder are mixed at a predetermined ratio; melting the powder material and injecting the powder material into a cavity of a powder molding die;
Cooling the mold to cure the material in a product shape, removing the cured product in the product shape from the mold, and heating the cured product to vaporize and remove the synthetic resin material component. A step of sintering the cured body from which the synthetic resin material component has been removed at a temperature near the melting point of the magnetic material, in this order.

The method of manufacturing a yoke according to the present invention may further have the following features. (2) the high-permeability magnetic material is permalloy, the synthetic resin material is polystyrene, and the predetermined ratio is approximately permalloy 8 and polystyrene 2 by weight ratio;
The electromagnetic device is an electromagnetic sounding body.

[0012]

FIG. 1 is a schematic process diagram of a powder injection molding method as an example of an embodiment of the present invention. First, permalloy powder (weight ratio of about 8) and polystyrene powder (weight ratio of about 2) are prepared as raw materials, and they are mixed and kneaded well in step 1. In step 2, an injection molding machine is prepared,
The mixture of raw materials is melted and supplied to an injection mold, filled into a shaped cavity of a product (finished part), and then cooled in the mold to cure the resin.

The product (semi-finished product) cured in step 3 is removed from the mold, and heated in a drying furnace in step 4 to vaporize and remove the resin component. Then, in step 5, the semi-finished product in which the metal fine particles are roughly bonded is sintered at a temperature close to the melting point of the metal material. Thus, a finished product having a predetermined dense composition is obtained. The semi-finished product slightly shrinks during the sintering process, but the ratio is determined by the processing conditions. The deformation by this processing method is also slight. These can be fully conditioned before mass production.

FIG. 2 shows the structure and operation of the injection mold used in step 2 of FIG. (A) is a cross-sectional view of a main part immediately before material injection showing a mold structure, and (b) is a cross-sectional view of a main part showing an operation of taking out a cooled and cured semifinished product. Reference numeral 10 denotes a fixed side cavity, which is a runner 1 which is a passage of the molten material.
0a. 11 is a movable side cavity, and a runner 1
0a has a product (semi-product) shaped cavity 11a connected to
Movable core pin 1 that determines the height H of the center pole
1b, ejector pin 11 for taking out a product (semi-finished product)
c. The runner stripper plate 12 covers the runner 10a during molding and moves when the runner is removed. Although not shown, the main part of the mold is provided with a heating device or a water passage for forced cooling.

After cooling the material, the process proceeds to step 3. FIG. 2 (b)
As shown, the movable cavity 11 and the runner stripper plate 12 are separated from the fixed cavity 10, and the semi-finished product 13 and the runner 14 (in this case, the hardened material inside the runner 10a, which is the passage of the molten material) are separated.
The ejector pin 11c projects the semi-finished product 13. The runner 14 is also taken out and collected. The semi-finished product is sent to step 4.

Although the embodiments of the present invention have been described above, it is needless to say that the present invention is not limited to the above-described embodiments. For example, the target product is not limited to the electromagnetic sounding body but may be a yoke member of a wide range of electromagnetic devices, the material of the magnetic metal powder to be used, the material of the synthetic resin material, the mixing ratio, the configuration of the mold, the temperature and time in each process. The management conditions and the like can be variously selected so that the effects of the present invention can be exhibited.

[0017]

According to the present invention, since the yoke is manufactured by the powder injection molding method, there is no need to use a plurality of dies for molding a single product, and there is no need for assembling. Since the reproducibility of the product is very small, the dimensional accuracy and deformation can be kept within an acceptable range by setting the conditions in advance, and there is no residual distortion due to processing, so there is no adverse effect on magnetic properties, and post-processing is also performed. Various effects such as being unnecessary were obtained.

[Brief description of the drawings]

FIG. 1 is a process chart in an example of an embodiment of the present invention.

FIGS. 2A and 2B show a structure of a molding die used in a step 2 of FIG. 1, wherein FIG. 2A is a sectional view of a main part, and FIG.

3A and 3B show a shape of an example of a yoke to be subjected to the manufacturing method of the present invention, wherein FIG. 3A is a plan view and FIG. 3B is a cross-sectional view.

FIG. 4 is a cross-sectional view illustrating an example of the structure of an electromagnetic sounding body including a yoke manufactured according to the present invention or the prior art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Yoke 1a Center pole 1b Flat plate part 2 Buzzer case 3 Lead frame 3a Exposed part 4 Drive coil 5 Permanent magnet 6 Vibrating plate 10 Fixed side cavity 10a Runner 11 Movable side cavity 11a Product (semi-finished) shaped cavity 11b Movable side core pin 11c Ejector pin 12 Runner stripper plate 13 Semi-finished product 14 Runner B Warpage of plate-shaped part H Height of center pole G Gap between diaphragm and center pole T Thickness of plate-shaped part

Claims (2)

[Claims] A step of mixing a magnetic material powder having a high magnetic permeability and a synthetic resin material powder in a predetermined ratio to form a powder material;
A step of melting the powder material and injecting it into a cavity of a powder molding mold, cooling the mold and curing the material in a product shape, and a step of taking out a cured product of the product shape from the mold. Heating the cured body to vaporize and remove the synthetic resin material component, and sintering the cured body from which the synthetic resin material component has been removed at a temperature near the melting point of the magnetic material, A method of manufacturing a yoke for an electromagnetic device, comprising: 2. The high-permeability magnetic material is permalloy, the synthetic resin material is polystyrene, and the predetermined ratio is approximately permalloy 8 and polystyrene 2 by weight.
2. The method of manufacturing a yoke of an electromagnetic device according to claim 1, wherein said electromagnetic device is an electromagnetic sounding body.