JPH02200322A - Mold and stock block for this mold - Google Patents

Abstract

PURPOSE:To obtain a mold or a stock block for a mold excellent in strength and wear resistance, good in workability and dimensional accuracy and poor in occurrence of cavities by machining Zn alloy wherein contents of Al, Cu, Mg are specified. CONSTITUTION:The composition of a mold is made up of Al: 12.1-30wt.%, Cu: 6-20%, Mg: 0.01-20% and Zn for the rest except inevitable impurities and, if necessary, at least one element selected from a group of elements such as Ti, Zn, Ni, Co, Mn, Li, Si, La is contained by 2% or under. Zn alloy containing this element is machined, an injection mold for plastic material, etc., and a stock block used for this mold are formed. This is suitable for an injection mold to perform some tens of thousands of shots.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a mold and a material block for the mold, and more specifically, the present invention relates to a mold and a material block for the mold, and more specifically, it is made by machining a zinc-based alloy of a certain composition, and has high strength and durability. The present invention relates to an injection mold that has excellent abrasion resistance, good workability and dimensional accuracy, and less occurrence of cavities, and a material block used in the mold.

[Prior Art] In the field of plastic injection molds, molds manufactured by machining steel blocks are used for large-scale mass production with more than a few dozen blade shots, and on the other hand, molds manufactured by machining steel blocks are used for large-scale mass production with more than a few dozen blade shots. A mold made of zinc-based alloy by sand casting is used as a prototype.

On the other hand, with the recent trend toward high-mix, low-volume production, there is a demand for a simple mold with a lifespan comparable to that of a shotgun.

In response to such demands, steel molds have the drawback of requiring a long time for machining, so they cannot respond quickly to flexible model changes.

Furthermore, a mold machined from an aluminum alloy has been proposed, but it has the disadvantage that cavities are likely to form in the ingot as the material block, so attempts have been made to roll this mold. However, in this case, there are restrictions on the size of the block to be rolled. Furthermore, there are other issues such as difficulty in repair welding that is required due to processing errors or design changes, cavities remaining in the center of the plate thickness even after rolling, and difficulty in achieving a mirror finish on the mold.

Furthermore, the zinc-based alloys for casting that have been used for small-scale trial production in the past - 4.1% by weight AJ for boat fishing - 3% by weight Cu - 0.05% by weight M4-Zn (trade name ZAS) The above requirements are not met because the lifespan is only a few thousand shots.

Furthermore, Japanese Patent Application Laid-open No. 63-135043 discloses high strength,
Casting molds using zinc-based alloys, which suggest high wear resistance, have been proposed. However, when this zinc-based alloy is used as a conventional casting mold, the above-mentioned ZAS alloy (
Unlike the product name (trade name), there is a problem in that nests are likely to form on and near the surface.

In addition, such casting molds, even if the shrinkage width is taken into account,
Dimensional errors of about 0.1 to 0.2# in the resulting mold are unavoidable, and due to poor dimensional accuracy, it cannot be used as an injection molding mold that requires fitting, and due to the characteristics of the casting method. For example, it is not possible to obtain a mold with a shape that widens at the end, such as a mushroom shape.
Another problem is that there are restrictions on the shape that can be obtained.

[Problems to be Solved by the Invention] The present invention has been made in view of the problems of the prior art, and it has high strength and excellent wear resistance, as well as good workability and dimensional accuracy. It is an object of the present invention to provide an injection molding die with less occurrence of cavities and a material block used in the die.

[Means to solve the problem]

The above objects of the invention are achieved by machining a zinc-based alloy block having a constant composition.

That is, the mold of the present invention is made of aluminum 12.1 to 5
iii%, copper 6-2DTJ amount%, magnesium 0.01
~0.20m11%, optionally at least 2% by weight of IN selected from titanium, zirconium, nickel, cobalt, manganese, lithium, silicon, lanthanum series elements, from a zinc-based alloy with the balance being zinc excluding unavoidable impurities. This is obtained by machining.

The zinc-based alloy used in the mold of the present invention must have the above-mentioned composition; if the aluminum content exceeds 30% by weight, the good weldability of the zinc-based alloy will be lost. At the same time, a T phase (Cu3ZnAji) is formed and becomes brittle. If the aluminum content is less than 12% by weight, there is a limit to the amount of copper that can be added, and there is a tendency that higher strength cannot be obtained.

Furthermore, if the copper content exceeds 20% by weight, casting defects of 50 μm or more are likely to occur inside the cast product, which is undesirable, while if it is less than 6% by weight, component segregation occurs during solidification of the zinc-based alloy, that is, aluminum There is a tendency for the particles to gather at the top, resulting in changes in mechanical properties in the height direction, and furthermore, it is not possible to impart the desired mechanical strength to the mold.

Magnesium is necessary to prevent intergranular corrosion in Zn-AJ alloys, but its content is 0.20ffI.
If it exceeds 0.01% by weight, the mold becomes brittle, and if it is less than 0.01% by weight, the effect of inclusion is small.

At least one selected from titanium, zirconium, nickel, cobalt, manganese, lithium, silicon, and lanthanum series elements is optionally contained in order to improve the mechanical strength of the mold, such as hardness, but 2.0 Even if it is contained in an amount exceeding % by weight, there is no further effect of its inclusion.

The mold of the present invention can be obtained by machining a raw material block made of the above-mentioned zinc-based alloy, but when the mold is obtained by casting a zinc-based alloy of the same composition, the mold of the present invention can be It is not possible to obtain a suitable mold.

That is, when a mold is obtained by casting as described in JP-A No. 83-85043, cavities occur on and near the surface of the mold as described above, and the injection molded product is damaged. Not only does this lead to quality deterioration, but the dimensional accuracy is poor and it cannot be used as an injection mold that requires fitting, and moreover, it is impossible to obtain a mold with a complicated shape.

A preferred example of the method for manufacturing the mold of the present invention is as follows.

First, a predetermined amount of each component is added to a graphite crucible or the like so that the composition falls within the above composition range, and is melted to obtain a zinc-based alloy having the above composition range.

Next, this zinc-based alloy is melted at 450 to 550°C and cast into a mold with a predetermined size to obtain the material block of the present invention.

The casting method used here preferably employs a top heat method in which the top part is heated and the bottom part is cooled, in order to avoid segregation of aluminum. Further, as the mold material, foundry sand can be used, but it is preferably a cast iron material, more preferably a carbon material such as graphite, or a ceramic material with a water-cooled pipe installed therein. When graphite or the like is used in this way, the mechanical strength of the mold obtained is such that the tensile strength is 2 to 9 r/m 2 Brinell hardness (Hs
) will improve by about 5.

Although the dimensions and shape of the material block of the present invention obtained in this manner are arbitrary, it is generally a rectangular parallelepiped with -sides of 100 to 11000j.

Next, this material block is subjected to mechanical processing such as electric discharge machining to obtain a mold of the present invention having a desired shape.

At this time, machining is performed taking care to ensure that the molding surface of the mold does not become within a few millimeters of the surface. Preferably, about 5 ml of the surface should be ground first.

This mold has a tensile strength of 32 kgf/jIII2 or more and a Brinell hardness (Ha) of 130 or more. The lifespan required for a mold varies depending on the shape of the mold and the type of thermoplastic resin used for injection molding, but for example, a mold in the shape of a precision gear made of polyacetal resin has a lifespan of 15,000 yen.
~20,000 shots are required, but this requirement requires a tensile strength of 32 kgr/1ttrx2 or more and a Brinell hardness (
Ha ) is achieved at 100 or more, preferably 105 or more. The mold of the present invention can fully meet this requirement due to the above-mentioned mechanical strength values.

In addition, the limit of cavities that are acceptable for the surface quality of injection molded resin is 50 μm or less per 100 cIi.
No more than 5. Since the material block of the present invention is also obtained by casting, cavities occur, but those with a diameter of 50 μm or more are limited to the surface and its vicinity. Almost no cavities are observed in the mold, and therefore, injection molded products using this mold do not suffer from defects caused by these cavities.

[Example] The present invention will be specifically described below based on examples and the like.

Note that the values in Table 1 are based on weight % unless otherwise specified.

Predetermined amounts of each component shown in Table 1 were added to a graphite crucible and melted to obtain a zinc-based alloy.

Next, this zinc-based alloy was put into a cast iron mold, and
A material block of 0am x 300aw x 30gam was cast. This casting used the top heat method, in which the upper part of the mold was heated with a burner.

After grinding the surface of this material block, a gear-shaped mold was obtained by milling, electrical discharge machining, etc.

The resulting molds were evaluated for tensile strength, Brinell hardness, presence or absence of aluminum segregation, quality of cavities, and quality of welding performance, and the test results are shown in Table 1. Further, in Example 3, lathe machining performance and electrical discharge machining performance were evaluated as machining performance, and the results are shown in Table 2.

The test methods for each of these evaluations are as follows.

(Test conditions) (1) Tensile strength (kgr/m”): Tensile speed law/win, temperature 60 by Instron tensile testing machine
“Measured at C.

(2) Brinell hardness (Ha): Measured using a Brinell hardness tester under a load of 1000 kg, held for 30 seconds, and at a temperature of 25°C.

(3) Presence or absence of segregation The aluminum at the top and bottom of the mold was analyzed, and those with segregation were classified as "Yes" and those without segregation were classified as "No."

(4) Condition of nests 2. Grind 10 mm inside the mold surface and observe it. If there are 5 or less micro-nests of 50 μm or more observed per 100 ci, it is considered good, and if there are 6 or more, it is considered bad. did.

(5) Welding performance: T
Welding was performed on the mold surface by IG welding, and the welded cross section was observed. Those with cracks or blowholes in the welded part were considered poor, and those with no cracks or blowholes were considered good.

(8) Lathe processing performance: Comprehensive evaluation of rotation speed, feed, and depth of cut.

(7) Electrical discharge machining performance: 5 under the conditions of voltage 60V and current 6A
The time required to machine a hole of 5 m x 50 JIII x depth of 20 mg + with a finished surface area of 28 μm was calculated.

Comparative Examples 6-7 Commercially available aluminum alloy blocks with the same dimensions as those used in Example 3 (J I S A 7075-T 61 material)
A gear-shaped mold was obtained by electrical discharge machining in the same manner as in Example 3 using a 545C steel block.

The tensile strength, Brinell hardness, and welding performance of each mold thus obtained were evaluated in the same manner as in Example 3, and the test results are shown in Table 1.

In addition, in Comparative Example 6, the mold was ground from the surface to the center and observed, the condition of the cavity was judged as good or bad, and the test results were used in the first test.
Shown in the table.

Furthermore, the lathe machining performance and electric discharge machining performance of each of the obtained molds were evaluated in the same manner as in Example 3, and the results are shown in Table 2.

Comparative Example 8 A gear-shaped mold having the same dimensions and shape as in Example 3 was produced by casting from the same zinc-based alloy as in Example 3.

The obtained mold had a dimensional error of about 0.1# with respect to the desired dimensions of Example 3. Further, six or more microscopic cavities of 50 μm or more were generated on the mold surface and near the surface, and the evaluation was poor.

Example 21 The surface of the zinc-based alloy material block used in Example 3 was
After grinding for 1 m, a mushroom-shaped mold was prepared by electrical discharge machining or the like.

The obtained mold has excellent dimensional accuracy, and has 5 or less microscopic cavities of 50 μm or more on the mold surface and near the surface.
The evaluation was good.

Comparative Example 9 By casting from the same zinc-based alloy as in Example 3,
! An attempt was made to manufacture a mushroom-shaped mold with the same dimensions and shape as No. 421, but manufacturing was difficult because the shape was wide at the end.

Table 2 As shown in Table 1, the molds of Examples 1 to 10 obtained by electrical discharge machining a material block made of a zinc-based alloy containing a certain amount of aluminum, copper, and magnesium were:
Compared to the molds of Comparative Examples 1 to 5 obtained by electrical discharge machining of material blocks made of zinc-based alloys outside the composition range specified in the present invention, the tensile strength and hardness are at a higher level. It had a hardness of over 32 kgf/m'' and a Brinell hardness (H8) of over 130, all of which exceeded the properties required for molds.Also, there was no segregation of aluminum and the condition of cavities was good, making it possible to weld. Performance was also good.Furthermore, as shown in Table 2, lathe machining performance and electrical discharge machining performance were also extremely excellent.

Examples 11 to 20 contain a small amount of components such as titanium in the zinc-based alloy used in Example 3, but as shown in Table 1, properties such as hardness are further improved. .

In Comparative Example 6, an aluminum alloy block was made into a mold by electrical discharge machining, etc., and as shown in Table 1, although the tensile strength and hardness were at a high level, there were still some cavities remaining inside. The condition of the nest was poor. In addition, many fine cracks were observed in the welded area, and the welding performance was poor.

Furthermore, as shown in Table 2, the workability of Example 3
It was inferior to.

In Comparative Example 7, a steel block was made into a mold by electrical discharge machining, etc., and as shown in Table 1, the tensile strength and hardness were at a high level, but as shown in Table 2, In addition, the machinability was significantly inferior to that of Example 3, and the electrical discharge machining performance required 12 times as long as that of Example 3.

In Comparative Example 8, a mold was made by directly casting a zinc-based alloy having the same composition as in Example 3, but the dimensional accuracy was poor.
In addition, nests were observed and the condition of the nests was poor.

Example 21 and Comparative Example 9 attempted to manufacture a mushroom-shaped mold with a shape that widened at the end. In this method, a mushroom-shaped mold with good dimensional accuracy and good nesting conditions was obtained.
Comparative Example 9, in which a zinc-based alloy with the same composition as 3 was directly cast.
However, a mushroom-shaped mold with a widening shape could not be obtained.

[Effects of the Invention] As explained above, the present invention, which is made by machining a zinc-based alloy with a certain composition, has strength and wear resistance that can withstand injection molding of 20,000 shots or more, and has excellent workability and dimensions. A mold with good precision and less occurrence of cavities and a material block used in the mold can be obtained.

This means that the mold of the present invention exhibits extremely high workability compared to molds obtained by machining conventional steel blocks, and can respond to flexible model changes.

In addition, the mold of the present invention not only exhibits higher machinability than conventionally proposed molds obtained by machining aluminum alloy blocks, but also has fewer remaining cavities and has dimensional limitations. It has the advantage of being free of welding problems and having excellent repair weldability.

Furthermore, the mold of the present invention has higher strength and wear resistance than the mold manufactured by casting a low-strength zinc-based alloy that has been conventionally used for prototypes, and also has higher strength and wear resistance. 65(
For molds manufactured by casting high-strength zinc-based alloys such as those described in Publication No. 143, the formation of cavities is within the permissible limit and the dimensional accuracy is good, so it is possible to make parts that can be fitted. It has the advantage that it can be manufactured and that molds with a shape that widens at the end can be manufactured.

Therefore, the mold of the present invention is suitable as a mold for injection molding of a variety of currently required shots.

Claims (1)

[Claims] 1. Consisting of a zinc-based alloy consisting of 12.1 to 30% by weight of aluminum, 6 to 20% by weight of copper, 0.01 to 0.20% by weight of magnesium, and the balance excluding unavoidable impurities being zinc. ,
A mold made by machining. 2. Consisting of a zinc-based alloy with 12.1 to 30% by weight of aluminum, 6 to 20% by weight of copper, 0.01 to 0.20% by weight of magnesium, and the balance excluding unavoidable impurities being zinc;
A material block for molds that is machined. 3. At least 12.1 to 30% by weight of aluminum, 6 to 20% by weight of copper, 0.01 to 0.20% by weight of magnesium, titanium, zirconium, nickel, cobalt, manganese, lithium, silicon, and lanthanum series elements. A mold made by machining and made of a zinc-based alloy containing 2% by weight or less of type 1, the balance being zinc except for unavoidable impurities. 4. At least 12.1 to 30% by weight of aluminum, 6 to 20% by weight of copper, 0.01 to 0.20% by weight of magnesium, titanium, zirconium, nickel, cobalt, manganese, lithium, silicon, and lanthanum series elements. A material block for molds made of a zinc-based alloy containing 2% by weight or less of type 1, the balance being zinc except for unavoidable impurities, and machined.