JP4274464B2 - Injection mold having local pressure structure and injection molding method - Google Patents

Description

  The present invention provides an injection provided with an annular sleeve piece and a plurality of rod-like pressure transmission pins provided for pressing the annular sleeve piece in order to pressurize the surface in the lateral direction against the axial hole of the injection molded product. The present invention relates to a molding die and a method for molding an injection molded product using the die. If the mold is used, an injection molded product with less shaft hole blur can be obtained.

  Conventionally, in order to obtain a highly accurate resin injection molded product, for example, a resin gear, as shown in FIG. 1, a plurality of rod-shaped local processing members are used to locally pressurize the side surface (web) 15 ′ of the gear 10 ′. The pressure pins 26 (four in FIG. 1C) were provided, and the pressure pins 26 were partially pressurized only by the tip portions of the local pressure pins 26. For this reason, there is a problem in that the portion pushed by the local pressure pin 26 is pressurized, and the other portion of the side surface 15 ′ is distorted.

Japanese Patent Application Laid-Open No. 2002-235835 discloses a method of uniformly pressing a ring-shaped portion on the web 15 ′ of the gear 10 ′. (See Patent Document 1).
In this technique, a local pressure pin 36 that can be pressed in a part or circumferential direction on the web 15 'is used, and the center pin 12 is installed at a position where the molded product gear 10 is located more than the position where the local pressure pin 36 is installed. It is listed at a position close to '.
Therefore, when a part of the web 15 'is pressed in a dotted manner, there is a problem similar to that shown in FIG. 1, or a ring-shaped local pressurizing the ring-shaped part 15' uniformly. When the pin 36 is used, there is a problem that the center pin 12 is not sufficiently fixed, the center is shaken, and the accuracy of the center shaft hole 10a of the gear is likely to occur.

In addition, as shown in FIG. 2, there is a technique in which a web 15 'is pressed in a ring shape with a cylindrical tip surface 46a using a cylindrical local pressure sleeve 46.
However, in this technique, the distance between the portion 12b to which the center pin 12 is fixed and the gear 10 ′ is increased, and the distance between the mold circle and the cylindrical local pressure sleeve 46 or the local pressure sleeve 46 is increased. Since there is a need for a gap between the center pin 12 and the center pin 12, there is a problem that the center of the long center pin 12 is distorted and the accuracy of the shaft hole 10a of the gear tends to be poor.

JP 2002-235835 A (claims 8 and 9, paragraph number [0009])

  An object of the present invention is to improve the position accuracy of a center pin and obtain a highly accurate injection molded product in a local pressurizing mold for injection molding.

  As a result of intensive studies, the inventor has determined that the annular sleeve piece 4 that presses the surface 15 formed laterally with respect to the center pin 12 concentrically with the center pin 12 and the annular sleeve piece 4 at a plurality of points. It has been found that the above problem can be solved by using the local pressure pin 1 composed of a plurality of rod-shaped pressure transmission pins 5 for pushing in a distributed manner, and the present invention has been completed.

That is, the present invention provides an injection molding die to obtain a molded article 10 having a lateral surface 15 against a columnar shaft hole 10a and the shaft hole 10a, the columnar for forming the axial hole 10a Center pin 12, and, for pressurizing the surface 15, the pressure of a plurality of bar-like provided for pushing the center pin 12 concentrically with the annular sleeve piece 4 is provided in an annular and annular sleeve piece 4 An injection mold having a local pressure pin 1 made up of a transmission pin 5 , wherein the annular sleeve piece 4 and the pressure transmission pin 5 are formed integrally or integrally. And an injection molding method using the injection mold .
Fixing portion 12b of the center pin 12 is rod-shaped is preferably provided at a position closer to the molded article 10 than the fixed portion 5b of the pressurized pressure transmission pin 5, the pressurizing pressure transmission pin 5, the fixed portion 12b of the center pin 12 Is preferably provided so as to penetrate through.
Further, the local pressure pin 1 can also be used for protruding the molded product 10.
The injection mold of the present invention is particularly suitable when the molded product 10 is a resin molded gear .

  According to the present invention, the position accuracy of the center pin in the local press mold for injection molding is improved, and a highly accurate injection molded product can be obtained.

The injection-molded product 10 according to the present invention has a columnar shaft hole 10a and a surface 15 that is transverse to the shaft hole 10a, preferably a cylindrical molded product, and more preferably a cylindrical product such as a gear. It is a molded product.
The surface 15 transverse to the shaft hole 10a may be perpendicular to the shaft hole 10a or may have an inclination. The surface 15 may be a flat surface or a curved surface. On the top, patterns such as ribs, bosses, grooves, holes, and other textures, characters, symbols, and the like may be provided.

Hereinafter, the present invention will be described with reference to the drawings, but the present invention is not limited thereto.
FIG. 4 is a longitudinal sectional view of an example of a mold provided with the local pressure pin 1 of the present invention. The mold is provided with a center pin 12 for forming the shaft hole 10a and a local pressing pin 1 for pressing the surface 15.
The local pressurizing pin 1 according to the present invention includes an annular sleeve piece 4 for uniformly pressing the surface 15 and a plurality of rod-like pressurizing elements for pressing the annular sleeve piece 4 at a plurality of points in a distributed manner. It consists of a transmission pin 5.
The local pressure pin 1 can also be used for protruding a molded product from a mold cavity. Therefore, the pressurized pressure transmission pin 5, or are to be Ruigo respect to the annular sleeve piece 4, or annular sleeve piece 4 and a plurality of pressurized pressure transmission pin 5 must have Rukoto are manufactured integrally It is. Further , the end portion 5b of the pressure transmission pin 5 may pass through the fixed end 12b of the center pin 12 and then be fixed to the base portion.

  FIG. 3 is a longitudinal sectional view of an example of a mold provided with the local pressure pin 1 of the present invention. As shown in FIG. 3, instead of penetrating the fixed end 12b of the center pin 12, the end 5b of the rod-shaped pressure transmission pin 5 passes through the female mold 20a to which the center pin 12 is fixed, You may make it fix to.

  In the present invention, the fixing portion 12b of the center pin 12 is preferably provided at a position closer to the molded product 10 than the fixing portion 5b of the rod-shaped pressure transmission pin 5. By doing so, the shake at the time of setting the center pin 12 and filling the resin is suppressed, and the molding accuracy of the shaft hole is improved.

The shaft hole 10a of the injection molded product 10 may be a bottomed hole or a through hole, and the shape of the hole (generally referred to as a hole including a hole in the present invention) may be a polygon such as a circle, an ellipse, or a regular square. .
The length of the shaft hole 10a is preferably 0.2 to 2.0 times as long as the cylindrical side or the cylindrical diameter is 1.

The annular sleeve piece 4 is coaxial with the center pin 12 and is preferably a similar annular shape to the surface 15 of the cylindrical injection-molded article 10, and the surface of the ring that presses the surface 15 is preferably a flat surface. is there. The surface opposite to the surface that pushes the surface 15 of the ring may be a simple plane because it is pressed by the rod-shaped pressure transmission pin 5, but the bottomed hole in which the tip of the rod-shaped pressure transmission pin 5 can be accommodated in the plane. May be provided.
The annular area A for uniformly pressing the surface 15 is not particularly limited, but is preferably 1 to 5 times the total number of pins in the area B where one of the pressure transmission pins 5 presses the surface 15, that is, When n is the number of pins, A = (n × B) is 1 to 5 times. The height of the ring of the annular sleeve piece 4 is preferably 0.2 to 2.0 times as long as the length of the shaft hole 10a is 1.
The annular sleeve piece 4 may be divided into two or more, but is preferably one.

In order to uniformly pressurize the surface of the annular sleeve piece 4 of the pressure transmission pin 5, a plurality of rod-shaped pressure transmission pins 5 are provided, and the number thereof is not particularly limited as long as it is two or more. These arrangements are preferably arranged at the vertices of a regular polygon such as a regular triangle or a regular square. The cross-sectional shape of the pressure transmission pin 5 may be round or square, and the shape is not limited. The local pressurization may be performed on the entire surface 15 or a part of the surface 15, but is preferably performed uniformly in the circumferential direction. FIG. 4C shows a case where the four pressure transmission pins 5 are arranged at the vertices of a regular square.
A screw may be formed at the tip of the pressure transmission pin 5 so that it can be accumulated on the annular sleeve piece 4.
The diameter of the pressure transmission pin 5 is 20 to 100% of the width of the ring of the annular sleeve piece 4.

Hereinafter, a gear will be described as an example.
The resin-molded gear 10 ′ includes a rim 11 ′ formed in a cylindrical shape, teeth 13 ′ formed outwardly with respect to the central axis 12 ′ on the outer peripheral surface of the rim 11 ′, and a center on the inner peripheral surface of the rim 11 ′. It consists of a web 15 ′ extending in the shape of a flat disk in the axial direction, and bosses 16 ′ joined to the web 15 ′ and formed at the central axis. The position where the web 15 'is provided may be in the middle, upper part or lower part of the cylindrical part of the rim 11'. The bosses 16 'may be bosses or shafts.

  The web 15 ′ is a flat disk shape and is joined to the inner peripheral surface of the rim 11 ′ and the outer periphery of the boss 16 ′. The flat disk-shaped web 15 ′ may be provided with one or a plurality of through-holes, recesses, ribs, etc. in the flat disk-shaped part as required.

The molding method of the present invention may be a method in which local pressure is applied to normal injection molding, or a method in which local pressure is applied to the boundary between the mold cavity surface and the molded product. The former method includes a method in which a part or the whole of a mold is mechanically pressurized using a pressurized fluid such as a gas or a liquid or power of a motor or the like. Examples thereof include a method in which a pressurized fluid such as a gas or a liquid is directly pressed into the boundary surface between the cavity surface and the molded product.
An example of resin filling and local pressurization is shown. Using a normal injection molding machine, the molten resin is filled into the mold cavity from the cylinder side through the gate 35 '. For example, a pin gate is used as the gate 35 ′. The position of the gate is not particularly limited, and may be the lower surface of the boss, the side surface, or the web. Further, the number of gates is not particularly limited, and may be 1 to 5 or 6.
The local pressurization may be performed on the entire surface or a part of the flat disk-shaped web 15 ′, but is preferably performed uniformly in the circumferential direction.
The portion to be pressed may be, for example, a ring-shaped portion 15 ″ formed between two circles concentric with the central axis 12 ′ on the web 15 ′.

From the start to the end of pressurization of the web 15 ′, it is performed within a period of time T3 from the start of resin filling to the start of mold opening.
There is no particular limitation on the timing of pressurization, but when the web 15 ′ is pressurized at the same time as the injection, shrinkage deformation after pressurization occurs, so the internal resin near the intersection of the rim 11 ′ and the web 15 ′ solidifies. Immediately before.
In addition, holding pressure is performed after filling the resin, but there is no particular limitation on the injection holding pressure and the pressure applied to the web 15 ', but when the injection holding pressure is lower than the pressing pressure, the molten resin is pressed by pressurization. May flow back to the cylinder side from the gate 35 ', so that it is desirable that the pressurization timing is after the gate portion is solidified.
The gate portion may be mechanically sealed after filling with the resin.
The pressurization end time of the web 15 ′ is not particularly limited as long as it is until the mold opening starts. The time required from the start to the end of pressurization of the web 15 ′ is determined by the optimum value depending on the dimensions of the molded product, the type and temperature of the resin, the mold temperature, and the like.

Examples of the resin molded gear 10 ′ according to the present invention include a spur gear, a helical gear, a helical gear, a quick bevel gear, a spiral bevel gear, and a helical gear. The twist angle of the teeth is not particularly limited.
These helical gears and spur gears may be a single gear, a two-stage gear, or a combination gear that is combined in multiple stages from the drive motor and decelerates without rotational unevenness.

Examples of the material for molding the molded product 10 include resins, natural materials, and inorganic materials.
There is no restriction | limiting in particular as a kind of resin, if it can be used for injection molding, Preferably a thermoplastic resin is used. The thermoplastic resin may be any kind of resin such as crystalline resin, non-crystalline resin, biodegradable resin, non-biodegradable resin, synthetic resin, natural resin, general-purpose resin, engineering resin, polymer alloy, etc. .
General-purpose thermoplastic resins include polyethylene (PE), polypropylene (PP), poly-4-methyl-pentene-1, polyolefin such as polycyclic olefin, polystyrene (PS), AS resin, ABS resin, polyvinyl chloride (PVC) ), Polyacrylonitrile (PAN), (meth) acrylic resin, cellulosic resin, elastomer and the like.
Examples of the thermosetting resin include phenol resin, epoxy resin, polyurethane, rubber, unsaturated polyester, urea / melamine resin, and silicone resin.
Engineering resins include various aliphatic polyamides such as nylon 6, 6, 6, 12 and 6, 12, or aromatic polyamide (PA), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene Aromatic polyester resin such as phthalate (PEN), polycarbonate (PC), polyacetal, polyphenylene ether (PPO), polyarylene sulfide (PAS) such as polyphenylene sulfide (PPS), polysulfone (PSu), polyimide (PI) ), Liquid crystal polymer (LCP) such as liquid crystal polyester and liquid crystal polyamide, and fluorine resin.
In addition, aliphatic polyesters from aliphatic dicarboxylic acids, aliphatic diols, aliphatic hydroxycarboxylic acids or cyclic compounds thereof, and biodegradable resins such as aliphatic polyesters whose molecular weight is increased by diisocyanate, etc. Also good.

When molding a gear, for example, polyacetal resin (polyoxymethylene resin (POM)), polybutylene terephthalate resin (PBT) or polyethylene terephthalate resin (PET) can be used particularly preferably. Furthermore, polyphenylene sulfide resin, polyamide resin, etc. can also be used suitably.
These resins may be blended with various additives that are usually added, or may be a resin composition mainly composed of these additives.

The polyacetal resin may be either a homopolymer or a copolymer. In the case of a copolymer, in order to stabilize the main chain, a monomer component such as ethylene oxide or dioxolane is randomly copolymerized, a block or graft polymerized component, or a third component is introduced. Any form of copolymerization such as rice cake may be used.
Polyester resins such as polybutylene terephthalate and polyethylene terephthalate, in addition to the usual aromatic dicarboxylic acid component and aliphatic diol component, aromatic or aliphatic polybasic acids such as isophthalic acid, naphthalenedicarboxylic acid and adipic acid, or Further, it may be a copolymer obtained by modification using an alkylene glycol such as ethylene glycol or diethylene glycol or neopentyl glycol or an aromatic hydroxy compound such as bisphenol A as a glycol component.

Examples of natural materials as molding raw materials other than resin include wood powder, starch, and sludge powder.
Examples of the inorganic material as the forming raw material include iron powder and aluminum powder for sintered steel making parts, carbon powder for electrodes, and other glass powders.

  Shake of the shaft hole of the injection molded product obtained by the present invention is 0 to 0.02% of the diameter of the molded product, particularly in the case of gears, and 0.1 to 0.1% in the conventional product. As large as 0.8%.

(Example)
[Example 1]
As an example of the resin molded gear, a helical gear was molded. The helical gear has teeth 13 'formed outwardly and obliquely with respect to the shaft hole 10a on the outer peripheral surface of the rim 11' formed in a cylindrical shape, and the inner peripheral surface of the rim 11 '. The web 15 'extends in a flat disc shape and is joined to the outer peripheral surface of the cylindrical boss 16' (not shown).
As the resin, Duracon M270S (unfilled) manufactured by Polyplastics Co., Ltd. was used. The shrinkage rate during molding of the resin is 1.8%.
The design dimensions of the helical gear are: shaft hole diameter 6.0 mm, shaft hole length 15.0 mm, tooth outer diameter D 30 mm, tooth width b 15 mm, helix angle 20 degrees, module 1.0 It is. That is, the pitch circle tooth thickness S is 1.57 mm, the rim thickness Sr is 2.5 mm, the web thickness Su is 3.0 mm, and the thickness of the boss 16 ′ is 2.0 mm.
A gear having this size has not only sufficient strength and rigidity, which are conventional requirements, but also recent requirements such as initial accuracy, low noise performance, and high speed performance.

Based on the above design dimensions, a gear nest was produced by a normal method and assembled into a helical gear mold 20 incorporating the local pressure pin 1 shown in FIG.
Center pin: Length 50.0mm, outer diameter 6.0mm
Annular sleeve piece: outer diameter 20.0mm, inner diameter 10.0mm, height 20.0mm
Pressure transmission pin: Four 150.0 mm long and 4.0 mm outer diameter In order to reduce the rotational resistance of the gear nest, the die 20 has a radial roller bearing inside and outside the nest, and a thrust roller in the mold clamping direction. It incorporates a bearing.
The resin is press-fitted into the cavity of the mold 20 from three pin gates 35 provided at equal intervals in the circumferential direction on the upper surface of the boss of the gear.
For pressurization of the web 15 ′, the local pressurizing pin 1 advances at an arbitrary timing between the start of injection and the cooling process.

Α100iA manufactured by FANUC was used for the injection molding machine. The injection conditions are: cylinder temperature: 190 ° C., mold temperature: 60 ° C., injection speed: 20 mm / s, holding pressure: 100 MPa, injection holding time: 20 s, cooling time: 10 s. Moreover, the local pressurization conditions are a pressurization area of 2.3 cm ² and a pressurization load of 2.1 ton, and the applied pressure at this time is about 90 MPa.
After pressurizing for 1 s 19 seconds after the start of injection (that is, immediately before the inside of the molded product was solidified), the gear was taken out from the mold. As for the accuracy of each part of the gear, the shaft accuracy was measured by a roundness measuring device Talirond 300 manufactured by Taylor Hobson, and the others were measured according to the JIS B1702 (1976) accuracy measurement conditions for helical gears.
Shake of the shaft hole of the injection molded product was 5 μm.

[Comparative Example 1]
The same procedure as in Example 1 was performed except that a mold having a local pressure pin and a center pin shown in FIG. 1 was used.
Center pin: Length 50.0mm, outer diameter 6.0mm
Local pressure pin: 4 length 170.0mm, outer diameter 4.0mm

[Comparative Example 2]
The same procedure as in Example 1 was performed except that a mold having a local pressure pin and a center pin shown in FIG.
Center pin: length 300.0mm, outer diameter 6.0mm
Sleeve: Outer diameter 20.0mm, inner diameter 10.0mm, length 260.0mm
Gap: 0.005mm outside, 0.005mm inside
The results are summarized in Table 1 together with Example 1.

(A) It is a longitudinal cross-sectional view of the metal mold | die provided with the conventional local pressurization pin. (B) In said (a), it is a longitudinal cross-sectional view of the metal mold | die which shows the state by which the molded article was protruded. (C) It is AA sectional drawing of said (a). It is a longitudinal cross-sectional view of the metal mold | die provided with the conventional cylindrical local pressurization sleeve. It is a longitudinal cross-sectional view of an example of the metal mold | die provided with the local pressurization pin concerning this invention. (A) It is a longitudinal cross-sectional view of another example of the metal mold | die provided with the local pressurization pin concerning this invention. (B) In said (a), it is a longitudinal cross-sectional view of the metal mold | die which shows the state by which the molded article was protruded. (C) It is BB sectional drawing of said (a).

Explanation of symbols

1 local pressure pin 4 annular sleeve piece 5 (rod-shaped) pressure transmission pin
5b (Pressure transmission pin 5) fixing part
10 Injection molded products
10 'gear
10a Shaft hole
12 Center pin
12b (center pin 12) fixing part
15 surface (lateral to shaft hole)
15 'Web
20 mold
20a Female mold
20b Male mold
26 Bar-shaped local pressure pin
35 Gate
46 Local pressure sleeve (cylindrical)
46a End face of local pressure sleeve 46
46b Fixed part (of local pressure sleeve 46)

Claims (6)

In an injection mold for obtaining a molded product 10 having a columnar shaft hole 10a and a surface 15 lateral to the shaft hole 10a,
Columnar center pin 12 for forming the axial hole 10a and,
For pressurizing the surface 15, consisting of the center pin 12 concentrically with the annular provided in the annular sleeve piece 4 and the pressurizing pressure transmission pin 5 of a plurality of bar-like provided to push the annular sleeve piece 4 An injection mold having a local pressure pin 1 , wherein the annular sleeve piece 4 and the pressure transmission pin 5 are formed integrally or integrally . The injection mold according to claim 1 , wherein the fixing portion 12b of the center pin 12 is provided at a position closer to the molded product 10 than the fixing portion 5b of the rod-shaped pressure transmission pin 5. Pressurizing pressure transmission pin 5 is provided through the fixing portion 12b of the center pin 12, the injection mold according to claim 2. Local pressurizing pin 1 is used to protrude the molded article 10, the injection mold according to any of claims 1 to 3. Molded article 10 is a resin molded gear, injection mold according to any of claims 1 to 4. Injection molding method characterized by using the injection mold according to any of claims 1 to 5.