JPH0220313A - Metallic mold for injection molding using low-expansivity metal - Google Patents

Abstract

PURPOSE:To enable molding with high accuracy to be achieved irrespective of nonuniformity in the temperature of a metallic mold or some variations in molding conditions, if only a mechanical working is conducted with high accuracy at room temperature, by constructing the mold by use of a specified low-expansivity metallic material. CONSTITUTION:A manifold 1 is formed of a metallic material having a coefficient of thermal expansion of not more than 5X10<-6>mm/ deg.C, in a passage for distributing a resin into a plurality of cavities 2a, 2b,... between a mold 4 and a mold 5. It is assumed that the distance from the center position of a manifold block to each of resin-ejecting port 6a, 6b,... is 400mm, and the manifold block is heated to 250 deg.C at the time of molding. Then, the positional deviation of each of the ports 6a, 6b,... between a room temperature of 20 deg.C and the molding temperature of 250 deg.C where the coefficient of thermal expansion of the metallic material is 5X10<-6>mm/ deg.C is 5X10<-6>X(250-20)X400=0.46mm, which is well contained in the range of a gate diameter, so that not any inconvenience is generated at the time of molding even under variations in the temperature of the manifold block or in the mold temperature.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is intended to solve problems such as resin leakage caused by expansion of the manifold block due to heating, gate pitch deviation, etc., which always occur in runnerless molds for thermoplastic resin. It is related to the mold structure and its steel materials, and also parts constituting the male and female mold parts of ultra-precision thermoplastic resin molds.
The present invention also relates to an injection mold in which a low-expansion metal material is used for the mold parts (cavity plate and core plate) for incorporating these parts.

[Prior art] Conventionally, runnerless molds have a mold structure as shown in Fig. 1, which is made of ordinary metal steel (S material, SCM material, NAC material, S'
It is made of KD material, etc.). This type of mold system is called a runnerless mold or a hot runner mold, and molten resin is supplied from the resin injection port 8 of a heated manifold 1, and is poured into a plurality of cavities 2a, 2a, and 2a through the manifold.
2b, . . ., each gate 3a, 3b, .

Between the upper mold 4 and the lower mold 5, there are a plurality of cavities 2a2b,
...is configured. Each cavity 2 is in the upper mold 4.
Gates 3a, 31+, connected to a, 2 b,...
···have. Manifold 1 is for each game 1□3
Resin discharge ports 6a, 3b, . . .
It is equipped with 6 b,... Torpedoes 7a and 7b each having a built-in heater are built into the resin discharge port (referred to as a gate chip) to maintain the temperature at a high temperature. Similarly, the manifold 1 also incorporates a car 1 to a ridge heater for heating. The manifold 1 is fixed to the mold 4 with bolts or the like, sometimes via a heat insulating material (riser pad).

During resin molding, the manifold block 1 is heated to an appropriate temperature in the state shown in FIG.
b, ... are also heated (200-350°C).

On the other hand, the mold parts of molds 4 and 5 are usually kept at a low temperature of 20 to 130°C. Resin is injected from the resin injection port 8 of the manifold 1 and distributed to the resin discharge ports 6a, 61], . . . from the resin discharge ports 6a, 6b, .
21], * is injected with resin.

In such a mold system, if ordinary steel is used for the cocoon bold block 1, 1. A gradual expansion occurs depending on the heating temperature, while the mold materials 4 and 5 kept at a low temperature
does not show much expansion, so deformation of the manifold 1 occurs due to thermal expansion during that time. As a result, resin leakage occurs at the resin discharge ports 6a, 6b, and so on.
Leads to trouble.

If you want to prevent the manifold from deforming, the current solution for installing Mayu Bold Blocks is to loosely tighten the bolts. Under such conditions,
A pitch shift occurs in the torpedoes 7a, 7b,...
As a result, the snoky resin is discharged from the gates 3a and 3.
b. I can't do it while...

At present, such a phenomenon becomes a bigger problem as the mold becomes larger.

The above phenomenon similarly occurs in a multi-gate mold (a mold in which a large molded product is provided with a large number of gates).

Cavity Components - The male and female components that make up the cavity (hereinafter referred to as cavity components) also suffer from thermal expansion problems. In other words, no matter how precisely a part is processed at room temperature, when it is actually molded, it is heated to 40 to 130°C, so dimensional variations occur due to the temperature difference between room temperature and use. do. Therefore, when designing a mold, dimensions must be designed taking into account temperature expansion. Furthermore, there is currently no way to control instantaneous local temperature changes caused by injection of material into the cavity during molding.

In general, a guide bin 81 and a guide bush 82 are attached to the cavity plate and the core plate (hereinafter referred to as plates), as clearly shown in FIG. 2, in order to maintain alignment accuracy when opening and closing the mold. Therefore, unless the fixed and movable sides of the mold are preferably adjusted to the same temperature, the mold will not close. If the guide pin 81 and the guide bush 82 are tightened with a large force, an unreasonable strain will occur between the guide pin 81 and the guide bush 82, making it impossible to maintain precision during manufacture.

[Problems to be Solved by the Invention] Each component of the mold system as described above is, for example, S
Conventional technology has been to use steel materials such as steel, SC material, SK material, SCM material, and NAC material. This type of steel has a thermal expansion coefficient of 11 to 1.3 x], O-6m
Due to the large size (m/℃), the dimensions during mold assembly and during use (
(heating conditions), the dimensional difference becomes large. Since the upper mold 4 and the lower mold 5 are used at low temperatures, the resin discharge port 6a is closed at room temperature.
, 6b, ... and game 1" 3a.

Even if 3I), . . . match, they will not match when the manifold block is heated. Therefore, when designing the mold system, it is important to ensure that the resin discharge ports 6 a, 6 b are not at room temperature but during molding.
,... and game) If the positions 3a and 3b match, it is necessary to determine the dimensions.

However, when designing a mold, it is not possible to precisely specify the temperature at which the molding will be performed. In other words, when designing a mold, we take into account the shape and thickness of the product, the characteristics of the resin used, etc., estimate the temperature at which the optimal molding condition can be obtained based on past data, and then discharge ports 6a, 6b,... and K1-3a, 31J,
. . . The dimensions are determined so that they match. Then, try actually using the mold, examine the quality of the product, and if it is bad, 1.-Peed 7a, 7b...
This can lead to damage to the mold or improper filling of the resin, requiring major work to be done to modify the mold.

The present invention has been made in view of these points, and its purpose is to create an injection mold using a low-expansion metal that does not interfere with molding even if the molding temperature is slightly changed. It is about providing.

[Means for Solving the Problems] In the present invention, in order to solve the above problems, the first
As shown in the figure, a plurality of cavities 2 are formed between the mold 4 and the mold 5.
In the channel for distributing the resin to a, 2 b, ..., the manifold 1 is formed of a metal material having a coefficient of thermal expansion of 5 x 10-6 u+m/'C or less. be.

In addition, in Fig. 1, mold 4 and mold 5 are 5×10-'m
The cavity component 6 in FIG.
1.71 and is characterized by being formed of a metal material having a coefficient of thermal expansion of 5 x 10-'+nu+/'C or less.

[Effect] Hereinafter, the effect of the present invention will be explained by citing specific numerical values.

Now, move from the center position of the manifold block to the resin discharge port 6.
The distance to a, 6 b, · is 400 mm, and the manifold block is heated to 250°C during molding. When conventional 555C steel material is used, the positional deviation of the resin discharge ports 6a, 6b, . . . between room temperature (20° C.) and molding temperature (250° C.) is calculated as follows.

t3x10-'x(250-20)x400""1.
1 9m+n In other words, a positional deviation of 1.19mm occurs. Cavity 2 a, 2 b, - game 1□ 3 a, 3 b,
・= is about 0.5 mm, then 1・-Peed 7 a,
7 The tips of b,... must be designed at a position where the diameter protrudes into the game 1 during machining. This is an impossible design.

On the other hand, if a low expansion material (2X 10-6mm/℃) is used, 2X10-6X(250-20)X4000.184m
m, and for (5X 10-6mm/℃) product, 5x10-'x
(250-20) x 4000.46 mm, which is within the range of the gate diameter, so it can be seen that no problem will occur.

Therefore, it can be seen that in the present invention, no inconvenience occurs during molding even if the temperature of the manifold block or the temperature of the mold is changed.

Furthermore, if a low expansion metal is used for the mold components 4 and 5 in FIG. 1 or the mold components 41 and 51 in FIG.
Demonstrate its effectiveness. Guide pins 81 and guide bushes 82 are usually attached to these parts in order to improve alignment accuracy, but the alignment accuracy can be maintained permanently.

For example, in Fig. 2, the pitch of the guide pins 81 is set to 300 mm.
If this is the case, the dimensional difference that occurs between the molds 41 and 51 when a temperature difference occurs in normal steel materials is as follows.

11α1 柘(13X 10-'a+m/℃) Temperature difference ('C) Amount of expansion ['nm] 5 0.01
95 10 0.0390 15 0.0585 20 0.0780 30 0.11.70 40 0.1560 In other words, the accuracy of the guide pin and guide bush in a normal mold is designed with a tolerance of 0.03+nm. ,
This shows that if a temperature difference of 10°C occurs between the mold members 41 and 51, the mold cannot be clamped.

On the other hand, the low expansion steel used in the present invention (2 x 10-6 m
m/℃ product) is used, the results are as follows.

Low μ'0■1 (2X 10-6mm/℃) Temperature difference [
℃) Expansion amount (m Ill : 15
0.003 10 0.006 15 0.009 20 0.012 30 0.018 40 0.024 50 0.030 In other words, even if the temperature difference between mold 41 and mold 51 reaches 50°C, the guide pin and guide bush without damaging the
This shows that type accuracy can be maintained over a long period of time.

Furthermore, when the cavity part is used in accordance with the present invention, its effects are exhibited when molding ultra-precision parts and the like.

For example, if the cavity parts 61, 71 of a mold for molding a spherical lens with a diameter of 50 mm are processed into the same shape using ordinary steel and low expansion steel, and the parts are molded at a mold temperature of 100°C, then ordinary steel ( 13X 10-6mm/℃), 50
x13xlO-6x (100-20) 0.052mm For low expansion steel (2X 10-6mm/℃), 50x
2x10-6x (100-20) 0.008vn, and while with ordinary steel the mold deforms as much as 52 microns in diameter, with the product of the present invention using low expansion steel, the deformation is only 8 microns. It can be seen that this effect is remarkable in ultra-precision molding.

Furthermore, in a mold for molding precision parts, by forming all parts that require dimensional accuracy of the mold from low expansion metal, it is possible to prevent the molded product dimensions from deviation from design values. If a metal material with a large coefficient of thermal expansion is used as in the past, the shape accuracy of the molded product will fluctuate from the design value every time the molding conditions such as molding temperature, mold temperature, material temperature, etc. are changed, so the molding conditions It can be said that it cannot be changed. Moreover, prediction of the shape of a molded product using complicated CAD/CAM has many errors, and the expense required for this, that is, the production cost I~ is usually large. This tendency is particularly strong in the field of optical lenses and the like.

On the other hand, if the mold is formed using a low-expansion metal material as in the present invention, as long as the mold is precisely machined at room temperature, the molding conditions can be adjusted even if the mold temperature is uneven. Even if there is some variation, highly accurate molding is possible.

As a material with a small coefficient of thermal expansion, Fe-36w4%N
i alloy, Fe-32u+t%Ni-5wL%Co alloy, etc., but the former has a thermal expansion coefficient of 1.2 x 10-
61/℃, the latter is 0,3 X 10-6uuo/'
C (low temperature range), and does not exhibit an expansion coefficient that is less than one-tenth that of ordinary steel materials, making it a suitable material for the present invention. In addition, those with a trace amount of carbon added to these basic formulations or those with improved machinability by adding sulfur can also be used in the present invention. Note that low expansion metal materials can be used as they are for the cavity components of the present invention, but if the structure is coarse or the hardness is insufficient, nickel, nickel alloys, copper, hard chromium, etc. It can also be used with plating.

[Example 1] A mold having the structure shown in Fig. 1 was manufactured using 355C material, and only the manifold block was manufactured using 64% F (・
- It was made from a free-cutting alloy made of 36iut% Ni with a small amount of carbon added.

[Example 2] 67u+t%Fe 32u+t%Ni-5u+t%C
A lens mold cavity component with a diameter of 5 Qmm was precisely manufactured by machining using an alloy material having a composition of O.

A cavity plate and a core plate were manufactured using a free-cutting alloy made by adding a small amount of carbon to 64w[%Fe36u+t%Ni]. Its configuration is as shown in FIG.

Various plastics were molded using the molds produced in Examples 1 and 2, and dimensional changes in the molds, durability, accuracy of molded products, etc. were examined. Among them, the results when polymethyl methacrylate was used are shown below.

Manifold block quantity conditions, manifold block length 300mm Heating temperature 250℃ Result: 555CO, 8
97111111 Invention product 0, 1
No abnormality was observed even after injection molding was performed 1000 times at an injection pressure of 72+nm order 1 1500 K g/cm2.

There were no problems with resin injection due to misalignment of the trouble gate and torpedo, or resin leakage due to expansion of the manifold block.

A temperature difference of 30° C. was applied between the moving side and the fixed side of the mold of Example 2, and the alignment accuracy was measured. While a normal mold could not be clamped, the mold of the present invention could be clamped without any problems. Of course, no damage to the guide pin or guide bush was observed.

Cavity carved swirl collar 1 [A cavity part was manufactured using Starbucks steel and the product of the present invention using the mold of Example 2, and the shape accuracy of the obtained molded product was measured.

The dimensions (diameter) of the target molded product are 49.85±0.0Q
5 man. In the case of Starbucks steel, the material temperature was varied by ±10°C and the mold temperature by ±10°C, resulting in a molded product outside the desired dimensional tolerance.

On the other hand, in the present invention, even if the material temperature was varied by ±15°C and the mold temperature was varied by ±30°C, a molded product within the tolerance was obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of one embodiment of the invention, and FIG. 2 is a sectional view of another embodiment of the invention. 1 is the manifold block, 2+1, 2b, · is the cavity, 3a, 3b,... is the gate, 4 is the fixed side mold, 5
6a, 6b, . . . are resin discharge ports, 7a, 7
b... is 1-peed, 8 is a resin injection port, 9 is a control plate, 10 is a male mold part, 11 is a lower mold plate, 12 is a spacer, 13 is an ejector pin, 14 is an ejector plate, 15 is the parting line, 21 is the sprue, 22 is the runner, 23
24 is a molded product, 24 is a sprue lock pin, 25 is an ejector plate, 26 is a spacer block, 27 is a cooling water port, 41 is a cavity plate, 51 is a core plate, 61.71 is a cavity part, 81 is a guide pin, 82 is a guide Showing Bush.

Claims (3)

[Claims] (1) In a runnerless thermoplastic resin injection mold designed with multiple cavities or multi-point gates, the heating block that keeps the plastic material in a molten state at all times has a thermal expansion coefficient of 5 x 10^-^6 mm/ An injection mold using a low-expansion metal characterized by being formed from a metal whose temperature is below ℃. (2) In a thermoplastic resin injection mold, the metal parts forming the cavity have a thermal expansion coefficient of 5 x 10^-^
An injection mold using a low-expansion metal, characterized in that it is made of a metal with a temperature of 6 mm/°C or less. (3) In a thermoplastic resin injection mold, the cavity plate and core plate have a thermal expansion coefficient of 5 x 10^
An injection mold using a low-expansion metal, characterized in that it is made of a metal with a temperature of -^6 mm/°C or less.