JP3247680B2 - Injection mold - Google Patents

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 a precision part having a through hole, and more particularly, to a method for manufacturing a precision part having a very narrow circular wall having a very thin through hole. The present invention relates to a mold structure for injection molding.

[0002]

2. Description of the Related Art Conventionally, precision parts having through-holes having a complicated three-dimensional shape have been manufactured by a large number of man-hours by a machining method such as cutting. Hereinafter, the present invention will be described using typical components as examples.

For example, a print head of a dot printer has a drive unit having a solenoid mechanism and a plurality of needles arranged on the circumference of the drive unit. The needles are inserted through guide holes of a plurality of needle guides. Are converged in a trumpet shape to the needle guide at the tip of the print head, and reciprocate with each curvature.

The guide hole of the needle guide for guiding the needle has an appropriate inner diameter with respect to the outer diameter of the needle, and has lubrication due to mechanical strength and surface smoothness that can withstand severe sliding of the needle for a long period of time. Therefore, the guide hole interval also affects the printing quality, so that it is necessary to provide the guide holes with high precision.

[0005] Therefore, this needle guide is made of ceramics having excellent mechanical strength and durability, and has heretofore been manufactured by making full use of powder press molding and machining. However, recently, as an improvement of these conventional processing methods, use of a powder injection molding method capable of efficiently producing a product having a three-dimensional complicated shape has been proposed.
No. 07646.

In the case of manufacturing a component having a through hole such as a needle guide made of ceramics by powder injection molding, a method according to the following example has been generally used.

First, a ceramic powder such as alumina or zirconia is kneaded with an organic binder such as wax or thermoplastic resin to obtain an injection molding material.

Second, the injection molding material is injection-molded into an injection mold by an injection molding machine to obtain a needle guide molded body.

Here, the molding die has a structure in which a molding pin for forming the guide hole is connected to the mold at both ends in the axial direction so that a molded product having the guide hole penetrated can be obtained. Injection was performed from a side gate in a direction perpendicular to the axial direction of the forming pin to obtain a formed body 40 in which both ends of the guide hole 43 were penetrated as shown in FIG.

Third, under air or nitrogen atmosphere,
The temperature is gradually raised to about ° C, and a degreasing treatment is performed to decompose and remove most of the organic binder to obtain a degreased body. The degreased body is sintered in the air to obtain a needle guide sintered body.

Fourth, unnecessary portions of the sintered body such as the gate material 47 and the material pool 49 are removed by grinding or the like, and the guide holes 43 are removed.
The inner surface finish and the finish of the tapered portion are finished by wire wrapping, and the edge is finished by brush wrapping to obtain the needle guide 41 shown in FIG. 4B.

As described above, in the conventional manufacturing method, the forming pin forming the guide hole is a forming die whose both ends in the axial direction are connected to the mold, and the forming material is perpendicular to the axial direction of the forming pin. Injection from a side gate in an appropriate direction to obtain a molded body having both ends of a guide hole penetrated.

[0013]

In recent years, in order to improve the printing quality of a dot printer, there is a strong demand for a print head having a remarkably increased number of dots, and a needle guide used in such a print head has a guide hole as narrow as possible. For example, in the case of a print head in which one character is composed of 24 dots, the thickness of the thin portion between the guide holes, that is, the guide hole interval is significantly reduced to about 50 μm.

However, there has been a problem that such a needle guide having a remarkably narrow guide hole interval cannot be provided by the above-mentioned conventional manufacturing method.

This is because the flow of the molding material flow 56 press-fitted from the side gate 58 changes the thin portion between the molding pins 53 as shown in the schematic flow diagram of the molding material in the conventional manufacturing method of FIG. , The flow is obstructed because the interval is too small, and the molding material flow 56 flowing on both sides of the molding pin row collides from both sides at the thin portion between the guide holes, and the weld line WL is formed. It is for forming.

The occurrence of the weld line is related to the ratio of the guide hole interval to the guide hole diameter, and if the ratio is less than one third, the occurrence becomes remarkable.

Due to this weld line, unevenness in density and poor filling of the molded body around the guide hole occur, and the hole diameter accuracy of the guide hole of the sintered body after firing, unevenness of the surface of the hole, or unevenness of the hole. Provision is difficult due to problems in strength and the like.

In order to solve the problem of the weld line, various measures have been taken, such as raising the temperature of the mold or the temperature of the heating cylinder of the injection material. Problems such as deterioration of the mold, deterioration of the molding material and deformation during the degreasing process, and the inability to recycle the sprue and runner portions have occurred.

In general, the roundness of the guide hole is determined by various defects in the thin portion of the peripheral wall of the guide hole, that is, partial filling due to generation of a weld line, uneven density, chipping of the hole, unevenness of the surface of the hole, and unevenness of the hole surface. Insufficient strength, uneven hole spacing, etc.
And the roundness improves as the number of defects decreases.

Accordingly, the present invention provides a powder injection molding
Suitable for manufacturing through-hole holding parts with excellent roundness of holes, such as when manufacturing needle guides made of ceramics, where the thin portion of the guide hole peripheral wall is less than one third of the guide hole and extremely narrow ceramic guides. It is intended to provide a mold for injection molding.

[0021]

SUMMARY OF THE INVENTION The present invention relates to an injection mold for injection-molding a part having a through-hole, comprising an introduction guide portion provided so as to seal all outlets of one of the through-holes. , And a forming pin for forming a through-hole.

[0022] More preferably the configuration of providing this introduction guide portion of the gate for filling the formed shape material.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Here, the introduction guide section is shown in FIG.
As shown in (a) and (b), a through hole formed on the exposed surface of the guide hole (hereinafter referred to as a through hole) 23 of the original guide 21 and located on the tip side of the needle. 23
It is provided to seal everything.

The height H of the introduction guide portion is determined by the distance D between the molding pins.
The flow rate R of the molding material is set to an optimum value to suppress the occurrence of weld lines, thereby providing a through-hole with excellent roundness.

Here, the flow ratio R of the molding material means a ratio of a flow amount which is a passing amount of the molding material which varies with the molding pin interval D for the same unit passage area, and the molding pin interval is large and substantially free. In other words, based on the flow rate under flow conditions that do not change the flow rate, the flow ratio is defined as R = 1.
It is expressed as 0, and when the molding pin interval D becomes narrow and the flow rate decreases, the flow ratio R is also expressed as a small value.

The width and depth of the introduction guide are set to be at least as large as the height of the introduction guide (W1 and W2) outwardly from the molding pin.

The weld line that has conventionally occurred is the first weld line.
In addition, since the flowing molding material has a high viscosity, it is difficult to flow between narrow guide holes, that is, between the guide hole forming pins. Second, since the flowing distance from the gate is long, the molding material is gradually cooled, and the viscosity is further increased. Since the molding materials become so high that the molding materials of different flows are hardly compatible with each other, they tend to occur particularly at the collision surface of the two flowing flows between molding pins having a low temperature. This tendency naturally becomes more remarkable as the flow ratio R becomes smaller.

In the present invention, a molding die is provided with a guide for introducing a molding material, and a gate for the molding material is provided on the introduction guide, so that the molding pin is formed in a direction perpendicular to the axial direction of the conventional molding pin. The material flow was changed to flow in a parallel direction.

The change in the direction of the flow of the molding material with respect to the narrow thin portion of the molding pin, that is, the flow parallel to the molding pin, changes the form of collision of the flow of the molding material, thereby significantly suppressing the occurrence of weld lines. are doing.

Also, the most important needle guide,
The molding material, which has the shortest flow distance and is not cooled, that is, has good flowability, reaches and fills a narrow thin portion near the tip of the forming pin corresponding to the thin portion of the tip of the guide hole located on the tip end of the needle. Therefore, it is more effective in suppressing the weld line.

Further, by changing the height of the introduction guide portion in accordance with the flow ratio R of the molding material, which varies with the guide hole interval, the flow direction of the molding material is intentionally controlled to some extent to reduce the occurrence of weld lines. Restrained. However, at a flow ratio R as small as 0.05 or less, suppression of the weld line becomes extremely difficult.

Hereinafter, the present invention will be described in detail with reference to the drawings and embodiments by taking a needle guide for a dot printer made of ceramics as an example, but the present invention is not limited thereto.

[0033]

(Embodiment 1) The manufacturing method according to the present invention is the first embodiment.
The atactic polypropylene, ethylene-vinyl acetate copolymer and paraffin wax were added to 100 parts by weight of zirconia powder having an average particle size of 0.5 μm at a ratio of 40:30:
A mixture obtained by adding 15 parts by weight of an organic binder having a ratio of 30 was kneaded at 100 ° C. for 1 hour with a pressure mixer,
After cooling, it is pulverized to obtain a molding material.

Second, after filling the molding material into a heating cylinder of an injection molding machine and keeping the temperature in the heating cylinder at 150 ° C. to bring the molding material into a molten state, a shrinkage due to sintering is expected in advance. In addition, a molding material is filled from the gate of the introduction guide portion using an injection molding die provided with an introduction guide portion on the tip end side of a molding pin for forming a guide hole, and the introduction guide portion 15 shown in FIG. Is obtained.

Third, the molded body is heated in a degreasing furnace to 500 ° C. at a rate of 20 ° C./hour in a nitrogen atmosphere to remove 97% of the organic binder to obtain a degreased body. The body is fired in the air at 1500 ° C. for 1 hour to obtain a sintered body.

Fourth, the introduction guide portion 15 of the sintered body is removed by grinding to expose the guide hole 13 as a through hole.
The completed needle guide 11 which is a part having a through hole shown in FIG.
Get.

When the dimensions of each part of the needle guide manufactured by the manufacturing method according to the above process were measured and the cross section of the thin part between the guide holes was observed, the dimensional accuracy of each part was 99.8% or more. No weld line or lack of filling is found in the thin portion between the guide holes, and the guide hole is expressed as a ratio of the maximum diameter to the minimum diameter with an excellent roundness of 99.8% or more. Met.

(Example 2) By the same manufacturing method as in Example 1, the molding pin interval D of the mold for providing the molded body shown in FIGS. 05-
The needle guide was manufactured by changing the height of the introduction guide portion so as to be in the range of 0.4 to 1 to 3 times the interval between the molding pins.

The roundness of the guide hole of the obtained needle guide was measured, and the height of the introduction guide portion where the roundness of the guide hole exceeded 99.8% at a flow ratio R corresponding to each molding pin interval. When the ratio of the height to the molding pin interval was determined, it was found that the optimum height was different depending on the flow ratio R as shown in FIG.

This means that the height of the introduction guide must be changed in accordance with the flow ratio of the molding material, that is, the interval between the molding pins if the same injection conditions are the same, but the height of the introduction guide is unnecessarily increased. When a large value is set, grinding and removal after sintering require a great deal of time and cost, and the flow parallel to the molding pin of the molding material, which is a feature of the present invention, is disturbed. Tend to be.

Generally, when the flow ratio R of the molding material is less than 0.05, molding is difficult, and when it is more than 0.4, the influence of the molding pin interval is small. The flow ratio of the molding material varies depending on the molding material composition, the mold temperature, the material temperature, the injection pressure, and the like even at the same molding pin interval.

Further, the shape of the molding pin may be a straight shape or a tapered shape. In the method of the present invention, a tapered shape having a narrow portion is particularly effective.

In the above embodiment, zirconia was used as the ceramic powder, but alumina, silicon nitride, boron nitride,
Good results were obtained even with a high-hardness ceramic material such as silicon carbide or a material obtained by combining a lubricant.

[0044]

By applying the injection mold of the present invention to a method for manufacturing a needle guide for a dot printer,
Needle with a guide hole that has almost no defects with excellent roundness because the molding material fills the gap between adjacent molding pins uniformly and sufficiently in a state of good fluidity, which can significantly suppress the occurrence of weld lines. Guides can be mass-produced, and a printer head with high printing density has been commercialized.

In addition, the dimensional accuracy is very good when the variation of the external dimensions is within 0.2%, the surface roughness of the guide hole is small, the secondary processing for finishing the inner surface of the guide hole is unnecessary, and the taper portion is formed. In the case where the holding pin was used, the secondary processing of the edge of the guide hole was unnecessary.

As described above, the parts having through-holes manufactured using the injection mold according to the present invention have functional characteristics such as dimensional accuracy and mechanical strength, and do not require secondary processing. This is a manufacturing method that is also excellent in productivity and economy.

[Brief description of the drawings]

FIG. 1 shows a molded article (a) having an introduction guide formed by an injection mold of the present invention and a completed needle guide (b).

FIG. 2 shows a top view (a) and a cross-sectional view (b) of a molded article of a needle guide molded by an injection mold according to the present invention.

FIG. 3 shows that, at various flow ratios R, the roundness of the guide hole is 99.
FIG. 4 is a diagram showing a ratio of the height of the introduction guide portion to the forming pin of more than 8%.

FIG. 4 is a view showing an example of a process of molding with a conventional injection molding die, showing a molded body (a) having a through guide hole and a completed needle guide (b).

FIG. 5 is a schematic view of a flow of a molding material molded by a conventional injection molding die.

[Explanation of symbols]

 10 molded body 11 needle guide 13 guide hole 15 introduction guide

Continued on the front page (72) Inventor Shigeru Saito 6-11-12 Honcho, Tanashi-shi, Tokyo Citizen Watch Co., Ltd. Inside Tanashi Factory (72) Inventor Kenichi Yoshioka 6-1-112, Honcho, Tanashi-shi, Tokyo Citizen Watch Co., Ltd. Tanashi Factory (72) Inventor Seiichi Nakamura 2-663 Funatsu, Kawaguchiko Town, Minamitsuru-gun, Yamanashi Prefecture Examiner at Kawaguchiko Seimitsu Co., Ltd. Tomoya Kato (56) References JP-A-63-207464 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B29C 45/26-45/44 B28B 1/24

Claims (2)

(57) [Claims] An injection mold for injection-molding a part having a through hole, an introduction guide portion provided to seal all outlets of one of the through holes, and an injection guide part for forming the through hole. And a molding pin. Wherein said gate for filling the molding material
The injection mold according to claim 1, wherein the mold is provided in an introduction guide portion .