JPH09234770A - Manufacture of mold for injection molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a complex core free from deterioration, heat strain, an oxide film, cracks, deformation, a defective fusion bond, etc., in the inner structure of a material due to welding and brazing by eliminating the welding and brazing of the end parts of engaging surfaces of inner and outer cores. SOLUTION: The inside diameter of an outside core 3 at a room temperature is formed to be smaller than the outside diameter of an inside core 2, and a groove 21 which forms a cooling medium channel 4 is formed on the engaging surface between the inside and outside cores 2, 3. Next, at least heating the outside core 3 or cooling the inside core 2 is carried out to make the inside diameter of the outside core 3 greater than the outside diameter of the inside core 2, and the inside core 2 is engaged with the outside core 3 to assemble a complex core 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an injection molding die used for molding a molded article having multiple walls, and more particularly, to a method for producing a composite core having an inner core and an outer core. The present invention relates to a method for manufacturing an injection molding die provided with a coolant channel.

[0002]

2. Description of the Related Art In molding a molded product having a double wall such as an aerosol cap or a cosmetic bottle cap, the composite core portion forming the double wall has a relatively small thickness and a small heat capacity, and Since it is surrounded by the molten resin injected into the mold from both sides, the temperature of this portion rises rapidly and is difficult to cool. Therefore, there was a problem that the number of shots did not increase and productivity was low at the beginning.

Therefore, in order to increase the cooling rate of the composite core and increase the number of shots, a mold having a composite core a as shown in FIG. 5 has been used. (See "Molds for Injection Molding" and "Basics of Mold Design" published by Plastics Age Co., Ltd.). This composite core a is designed to allow a coolant such as cooling water to pass between the outer surface of the inner core b and the inner surface of the outer core c, with the inner core b and the outer core c being narrowed (referred to as a blind eye). A coolant channel d is provided.

Further, a center core e having a small diameter tip is fitted inside the inner core b, and a cavity g is formed by the fixed side template f, the composite core a and the tip of the center core e.

FIG. 6 is a system diagram of the refrigerant flow path d in the composite core a shown in FIG. 5, in which the refrigerant is supplied from the refrigerant inlet j ₁ , cools the composite core a, and then is discharged from the refrigerant outlet j _2. . Further, a long hollow cooling tank h is formed in the center core e, the inside of the cooling tank h is partitioned by a partition plate i, and the refrigerant supplied from the refrigerant inlet k ₁ is on one side of the partition plate i of the cooling tank h. After passing through the tip of the partition plate i and passing on the opposite side, it is discharged from the refrigerant inlet k ₂ . During this time, the refrigerant cools the center core e. In this way, the molten resin injected into the cavity g is quickly cooled, so that the number of shots increases.

[0006]

By the way, in the conventional mold shown in FIG. 5, the inner core b and the outer core c are narrowed. Therefore, in order to prevent the refrigerant from leaking from the gap, the inner core b is prevented. The ends of the fitting surfaces of b and the outer core c are annularly welded or brazed like m and n. However, since the welded portion is locally heated above the melting temperature of steel, deformation, alteration of the internal structure of the material, cracks due to thermal strain, etc. may occur. In addition, cracks may also be generated from the oxide film or the welded portion due to welding, which may cause deformation of the mold. In addition, since the material of the brazing is different from that of the main body of the mold, they are not fused together, and the strength of the brazing is weak. In addition, since the linear expansion coefficient is different, the material sometimes separates from the material interface.

The present invention has been made in view of the problems of the prior art as described above, and is composed of an inner core and an outer core, and a refrigerant passage is formed on a mating surface of the inner and outer cores. A method for manufacturing an injection molding die having a composite core, which eliminates welding or brazing at the ends of the fitting surfaces of the inner and outer cores, and changes in the internal structure of the material due to welding or brazing, thermal strain It is an object of the present invention to provide a method for manufacturing an injection molding die that prevents the occurrence of oxide films, cracks, deformation, defective fusion, and the like.

[0008]

In order to achieve the above object, the present invention is a method of manufacturing an injection molding die having a refrigerant channel in the wall of a composite core composed of an inner core and an outer core. The inner diameter of the outer core at room temperature is smaller than the outer diameter of the inner core, and a groove is formed in the mating surface of the inner core and the outer core to form a refrigerant flow path. After performing at least one of the cooling of the core to make the inner diameter of the outer core larger than the outer diameter of the inner core,
The feature is that a composite core is assembled by fitting the inner core and the outer core together.

In the present invention, the inner diameter of the outer core and the outer diameter of the inner core at room temperature are the materials of the inner core and the outer core,
The temperature is determined by the heating temperature of the outer core or the cooling temperature of the inner core, the required leak pressure resistance, etc., but details will be described later in Examples.

The groove forming the coolant channel may be engraved only on the inner core side, on the outer core side, or on both. Examples of means for engraving the groove include mechanical cutting with a lathe, a milling machine, electric discharge machining, and a combination thereof.

The present invention is a method of assembling by so-called shivering (refer to JIS B0401 "Dimensional tolerance and hameai").
The outer core may be heated and expanded for fitting, the inner core may be cooled and contracted for fitting, or both.

As a method for heating the outer core, a method using an oven, an oil tank, a burner, electric heating or the like can be mentioned. As a method of cooling the inner core, a method of using an ordinary refrigerator or freezer, dry ice, liquefied nitrogen and the like can be mentioned.

(Operation) The inner diameter of the outer core is formed to be smaller than the outer diameter of the inner core at room temperature, and then the outer core is heated to expand, or the inner core is cooled to contract, or both. By doing so, the inner diameter of the outer core can be made larger than the outer diameter of the inner core.

When the outer core is fitted to the inner core in this state and then cooled to room temperature as it is, an attempt is made to restore the inner diameter of the outer core to be smaller than the outer diameter of the inner core. Contact stress is generated between them, and this contact stress provides high water tightness between the outer core and the inner core.

In addition, a groove is formed in the fitting surfaces of the inner core and the outer core, and the inner core and the outer core are fitted and assembled to each other, so that the inside of the wall of the composite core including the inner core and the outer core is assembled. It is possible to easily form the refrigerant flow path.

Since no welding or brazing is performed in the present invention,
The material is not locally heated to a high temperature, which results in internal texture alteration, thermal strain, oxide film, cracks, deformation,
Less likely to cause fusion defects.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described with reference to an example of manufacturing a cap molding die for an aerosol container by heating an outer core and cooling the inner core. FIG.
FIG. 3 is a partial cross-sectional view of the composite core of the mold along the axis.
In the composite core 1, the outer surface of the inner core 2 and the inner surface of the outer core 3 are fitted to each other, and the inner core 2 and the outer core 3 are fitted to each other. However, the composite core 1 shown in FIG. 1 is not welded or brazed to the ends of the mating surfaces of the inner core 2 and the outer core 3 as in the conventional composite core a shown in FIG. A groove 21 is engraved on the outer surface of the inner core 2 (see FIG. 2), and a groove 21 is left unengraved on the inner surface of the outer core 3 so that the inner core 2 and the outer core 3 are fitted to each other. A coolant channel is formed between the core 2 and the outer core 3.

A center core 5 is further fitted inside the inner core 2, and a cavity 7 is formed by the fixed side mold plate 6, the composite core 1 and the tip of the center core 5. Further, a long cylindrical cooling tank 8 is formed in the center core 5, the inside of the cooling tank 8 is partitioned by a partition plate 9, and the refrigerant supplied from the refrigerant inlet 101 is cooled by the cooling tank 8.
The partition plate 9 enters one side of the partition plate 9 and is discharged around the partition plate 9 from the refrigerant inlet 102, during which the center core 5 is cooled by the refrigerant.

The composite core of the present invention is manufactured in the following steps. The inner diameter D of the outer core 3 is formed smaller than the outer diameter d of the inner core 2 by a lathe. The specific size of each is cut according to the material of the outer core 3 and the inner core 2, the heating temperature of the outer core 3, the cooling temperature of the inner core 2, the withstand pressure required for the composite core 1, and the like. In addition, for the purpose of facilitating the fitting work, the inner surface of the outer core 3 and the inner core 2 may be as necessary.
The outer surface of is polished. Grooves 2 for forming a coolant flow path 4 on the outer surface of the inner core 2.
Engrave 1. (See FIG. 2. The step of may be performed before.) The outer core 3 is heated, the inner core is cooled, or both of them are performed. After stabilizing the outer core 3 and the inner core 2 at a predetermined temperature, the inner core 2 is fitted into the inner surface of the outer core 3. The outer core 3 and the inner core 2 are left to stand until the temperature reaches room temperature. The ends of the mating surfaces of the inner core 2 and the outer core 3 are not welded or brazed.

(Example) A cap molding die for an aerosol container having a composite core 1 having an inner core 2 and an outer core 3 as shown in FIG. 1 and having a fitting surface of 30 mm in diameter and 3 mm in thickness, respectively. Manufactured.

First, the cutting dimensions of the outer core 3 and the inner core 2 will be described with reference to FIGS. 3 and 4. Heating the outer core and cooling the inner core,
If you match fit an inner core and an outer core, for the inner core of the maximum outer diameter d _2max outside the core of the minimum inner diameter D _2min at the time of mating can be inserted, as shown in FIG. 3, D _2min ≧ d _2max ··· (1), and in order to have a crimp for preventing water from leaking after completion, the inner diameter D _1max of the outer core 3 and the outer diameter d of the inner core at room temperature
_As shown in FIG. 4, _{1 min} is D _1max <d _1min ...
It is necessary to be (2).

Therefore, according to JIS B 0401 (Dimensional tolerance and hame eye), the hole reference hame eye has a grade of H7 / h6, the tolerance of the inner diameter of the outer core is +0.021 mm, -0 mm (30 mm) for 30 mm. _2max = 30.02
1mm, D _2min = 30.000mm), the maximum gap is 0.034 mm, the minimum gap is 0mm next internal core, the outer diameter of the inner _{core, d 2max = 30.000mm, d 2min} = 30.
Become a 021-0.034 = 29.987mm, D _2min
The above condition (1) is satisfied at = d _2max .

Next, the outer core is heated to 150 ° C. in an oven, the inner core is cooled to −75 ° C. with dry ice, and then immediately fitted. Nevertheless, it is assumed that the temperature of the outer core drops to 120 ° C. and the temperature of the inner core 2 rises to −50 ° C. during the fitting operation. The inner core and outer core are made of steel (coefficient of linear expansion: 12 × 10 ^-6 ).
Then, when the inner diameter dimensional variation ΔD of the outer core from the fitting temperature 120 ° C. to room temperature is calculated, ΔD = 30 × 12 × 10 ⁻⁶ × (20−120) = − 0.036 mm 3) That is, contraction occurs. Similarly, the temperature at the time of fitting -5
Calculating the outer diameter dimensional variation Δd of the inner core from 0 ° C to room temperature, Δd = 30 × 12 × 10 ⁻⁶ × {20 − (− 50)} = 0.025 mm ··· (4) That is, expansion Becomes In addition, the maximum simeiro 2δ _max = -0.036- (0.025) = -0.061 mm, the minimum simeiro 2δ _min = -0.061-(-0.034 (maximum gap) = -0.027 mm From the above, the maximum inner diameter D _1max , the minimum inner diameter D _{1min of} the outer core, and the maximum outer diameter d _1max and the minimum inner diameter d _1min of the inner core at room temperature are: D _1max = D _2max −ΔD = 30.021-0 _{.036 = 29.985mm, D 1min = D} 2min -ΔD = 30.000-0.036 = 29.964mm, d 1max = d 2max + Δd = 30.000 + 0.025 = 30.025mm, d 1min = d 2min + Δd = 29.987 + 0.025 = 30.12 mm, and cut.

Further, the maximum shiroiro 2δ _max and the minimum shiroiro 2δ _min are as follows: 2δ _max = [ΔD-Δd] -minimum gap = 0.061-0 = 0.061 mm, 2δ _min = [ΔD-Δd] -maximum gap = 0.061-0.034 = 0.027 mm.

As a standard for evaluating the watertightness between the inner core and the outer core, the contact stress generated on the contact surface (fitting surface) in the double-barreled double cylinder was determined. The calculation is performed using the inner cylinder as the inner cylinder and the outer core as the outer cylinder.
("Mechanical Design Handbook": Ishiki Kiuchi, published by Nikkan Kogyo Shimbun).

[0026]

[Equation 1]

The symbol in Equation 1 is p _m : contact stress (kgf / c) generated on the contact surface (fitting surface)
m ² ) p ₁ : Inner cylinder inner pressure (kgf / cm ² ), p ₂ : Outer cylinder outer pressure (kgf / c)
m ² ), E ₁ : Inner cylinder longitudinal elastic modulus (kgf / mm ² ), E ₂ : Outer cylinder longitudinal elastic modulus (kgf / mm ² ), m ₁ : Inner cylinder Poisson's number, m
₂ : Poisson number of outer cylinder, 2r ₁ : Inner diameter of inner cylinder before fitting (mm), 2r ₂ : Outer diameter of outer cylinder before fitting (mm),
2r ₃ : Indicates the outer diameter (mm) of the inner cylinder before fitting, and 2δ is the interference (mm).

Here, p ₁ = p ₂ = 0, E ₁ = E ₂ = 2 × 1
0 ⁴ kgf / mm ² , 2r ₁ = 24 mm, 2r ₂ = 36 mm, 2r ₃ = 3
0 mm, 2δ _max = 0.061 mm, 2δ _min = 0.027
_{mm, m 1 = m 2 =} 3, as, contact stress p _{m max} at the maximum Interference 2.delta. _max, and when obtaining the contact stress p _{m min} when the minimum Interference _{2δ min, p m max = 4.03kgf} / mm ² (= 403 kgf / cm ² ), p _{m min} = 1.78 kgf / mm ² (= 178 kgf / cm ² ), and it can be seen that high contact stress can be obtained even at the minimum interference.

Further, as a result of actually conducting a water leak test of the composite core by applying a hydrostatic pressure of 10 kgf / cm ² to the refrigerant channel, no leak was observed at all.

[0030]

As is apparent from the above description, according to the present invention, a high contact stress is generated between the inner surface of the outer core and the outer surface of the inner core due to the interference fit, and the contact stress causes the composite core to have high watertightness. Is obtained. Therefore, there is no need to perform welding or brazing that is likely to cause deterioration or corrosion of the internal structure of the material, oxide film, thermal strain, cracks, and leakage of refrigerant due to them, and inexpensive and highly reliable injection molding A mold is obtained.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of a main part showing an example of an injection molding die manufactured according to the present invention.

FIG. 2 is a side view of an inner core of the injection molding die shown in FIG.

FIG. 3 is a schematic diagram showing a dimensional relationship between an outer core and an inner core during fitting.

FIG. 4 is a schematic diagram showing a dimensional relationship between an outer core and an inner core during cutting (normal temperature).

FIG. 5 is a partial vertical cross-sectional view of a main part showing an example of an injection molding die manufactured by a conventional technique.

FIG. 6 is a system diagram of a coolant flow path of the injection molding die shown in FIG.

[Explanation of reference numerals] 1 composite core 2 inner core 21 groove 3 outer core 4 refrigerant flow path

Claims (1)

[Claims] 1. A method of manufacturing an injection-molding die having a coolant passage in a wall of a composite core including an inner core and an outer core, wherein an inner diameter of the outer core at room temperature is smaller than an outer diameter of the inner core. Along with the formation of the inner core and the outer core, a groove is formed in the fitting surface of the inner core to form a refrigerant flow path, and then at least one of heating the outer core and cooling the inner core is performed to set the inner diameter of the outer core to that of the inner core. A method for manufacturing an injection-molding die, comprising assembling a composite core by fitting an inner core and an outer core together after making the outer diameter larger.