JP2000280056A - Semi-molten injection molding method of light metal member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably obtain a desired strength of a member by specifying the relationship between relative density and solid phase rate of a molding product so as to perform molding. SOLUTION: When a molten light metal is injected and charged in a molding cavity of a molding die under a semi-molten condition so as to obtain a molding product, molding is done under a condition that the formula ρ>=0.1×α+96 will be satisfied where relative density of a molding product is δ[%] and the solid phase rate is α [%]. The solid phase rate is proportion of the solid phase against the entire molten metal (solid phase+liquid phase) in the semi-molten metal, which is numerally found as proportion (area ratio) of the solid phase portion against the entire observed area by observing a solidification structure of the molding product after injection. In this case, it is preferable that molding is done at the solid phase rate of α>=5[%]. Therefore, absolute volume to be solidified/shrunk after injection is reduced so as to maintain the relative density high, and viscosity of the molten metal is maintained high to prevent entrainment of gas, resulting in restraining dispersion of the relative density due to gas failure or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semi-solid injection molding method for a light metal member in which a molten metal is injected in a semi-molten state into a molding cavity of a mold to obtain a molded product.

[0002]

2. Description of the Related Art For example, light metals such as magnesium (hereinafter, appropriately denoted by its element symbol Mg) and its alloy or aluminum (hereinafter, appropriately denoted by its element symbol: Al) and its alloy are used as materials. As a method of manufacturing a metal member, a so-called semi-molten product is obtained by injection-filling a molten metal in a semi-molten state (essentially less than the melting point) from an injection nozzle into a molding cavity of a mold. Injection molding methods are conventionally known (for example,
See JP-A-9-38758).

[0003] The semi-solid injection molding method is relatively clean (clean) in terms of working environment and higher in safety than the casting method such as a die casting method, and has high precision in quality. It is known as a process capable of obtaining a homogeneous light metal molded product. In addition, since the temperature of the molten metal (hereinafter, also referred to as “molten metal” even if it is in a semi-molten state rather than a completely molten state) is low, so-called “burr”
This is suitable for high-speed and / or high-pressure injection, which is advantageous in improving productivity. Furthermore, by injecting and filling the molten metal into the molding cavity in a semi-molten state, the molten metal in which the undissolved solid phase portion is mixed in the completely dissolved liquid phase portion is directly injected and filled, so that the flow is close to laminar flow. The gas is filled in a state, and the generation of gas defects due to the entrainment of the gas is relatively small.

[0004] In the present specification, the "semi-molten state" of a molten metal as a raw material to be injected is basically defined as "a solid state raw material (solid phase) is melted into a liquid state. "The state in which the raw material (liquid phase) coexists", which is usually a state obtained by heating the raw material to a temperature lower than its melting point. However, a case where the temperature of the molten metal is substantially at or just above the melting point and the solid phase ratio is substantially equal to 0 (zero)% is also included in the “semi-molten state”.
Even when the molten metal itself has such a substantially solid phase ratio of 0%, considering the actual injection molding process, one injection (one shot) from the injection nozzle into the mold is completed after the next injection (the next shot). Before the injection is performed, the molten metal in the molten metal supply path of the injection nozzle is cooled, and a solidified portion (a so-called cold plug) or a high solid portion having a high solid phase ratio is generated at the nozzle tip side. However, the molten metal actually injected into the molding cavity inevitably contains a solid phase portion.

[0005] In the present specification, the term "solid phase" refers to "a portion of a metal melt that is not melted and remains in a solid state when it is in a semi-molten state". Refers to "a part which is completely melted and is in a liquid state". By observing the solidified structure of the molded article after injection, the “solid phase” is referred to as a “part that has been maintained in a solid state without being melted in a semi-molten molten metal state”. The liquid phase portion, which was completely melted in the state to be in the liquid state, can be easily identified.
When the molded article is referred to as a “solid phase”, it refers to “a part that was maintained in a solid state without being melted in a semi-molten molten metal (solid phase)”. Further, in this specification,
The “solid phase ratio” refers to “the ratio of the solid phase to the entire molten metal (solid phase + liquid phase) in the semi-molten metal melt”. By observing the solidification structure of the molded article after injection, the observation area Percentage of area that was solid phase (area ratio)
Can be obtained numerically.

When a light metal member is manufactured by the above-mentioned semi-solid injection molding, the relative density of the member (the actual density with respect to the theoretical density expressed as a percentage (%)) is generally increased by increasing the solid phase ratio. It is said that it is possible to increase the mechanical properties such as tensile strength. Further, it is said that the higher the solid phase ratio of the molten metal, the more it is filled in a state closer to laminar flow during injection filling into the molding cavity, and the occurrence of gas defects and shrinkage cavities can be suppressed.

[0007]

However, actually, due to differences in various molding conditions such as the temperature of a molding die, the temperature or injection speed of an injection cylinder, and the holding pressure during molding, solid-phase Due to the difference in the average solid phase diameter even though the ratios are the same, furthermore, in many cases, the obtained molded product almost inevitably contains defects such as gas defects and shrinkage cavities. For this reason, even if the solid fraction is the same, a considerable difference (variation) occurs in the relative density and the tensile strength. Further, even if the relative density is the same, a considerable variation occurs in the tensile strength.

[0008] Therefore, when an attempt is made to obtain a certain tensile strength or more, the desired strength can be stably obtained even if only the solid fraction or only the relative density is set to a certain value or more. It is difficult. In this specification,
The “average solid phase diameter” refers to “the average value of the diameter of the equivalent circle of a portion of the semi-molten metal that is not melted and remains in a solid state”. This “average solid phase diameter” is obtained by observing the solidification structure of the molded article after injection, and calculating the “average of the equivalent circle diameter of the portion of the semi-molten metal that was not melted and maintained in the solid state. Value can be measured.

That is, in the case of a light alloy member such as a Δg alloy member, it is generally preferable that the material has a tensile strength of about 200 ° Pa or more for practical use.
JIS H 530 frequently used as alloy die casting
3 МD1 (Мg alloy die casting 1 type: ASTМ B94
230 МPa as reference value
It is said that it is more preferable to provide a higher strength than this. However, when it is attempted to secure such a strength by a semi-solid injection molding method, the solid phase ratio and the relative density (and, consequently, There is a problem that it is difficult to determine how to set the molding conditions).

Accordingly, an object of the present invention is to provide a molding method capable of more stably obtaining a desired member strength when molding a light metal member by a semi-solid injection molding method. .

[0011]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in view of the above technical problems, and as a result, by maintaining the solid phase ratio and the relative density in a specific relationship, the variation has been considered. However, a relative density equal to or greater than a certain value can be obtained for a predetermined solid fraction, and a relatively good interphase relationship can be obtained by using a parameter that combines the solid fraction and the relative density. Was found to be.

Therefore, the method for semi-molten injection molding of a light alloy member according to the invention of claim 1 of the present application (hereinafter referred to as the first invention) comprises injection-molding a molten light metal into a molding cavity of a mold in a semi-molten state. A semi-solid injection molding method for a light metal member, wherein a relative density of the molded product is ρ [%] and a solid phase ratio is α [%], and the relationship between the two is expressed as follows:
The molding is performed under the condition that ρ ≧ 0.1 × α + 96 is satisfied.

The invention of claim 2 of the present application (hereinafter referred to as the second invention)
The first aspect of the present invention, the solid phase ratio α
It is characterized in that molding is performed with setting to ≧ 5 [%].

The reason why the lower limit of the solid fraction (α) is set to 5% is that, when the solid fraction is less than 5%, the absolute amount of coagulation and contraction after injection increases and the relative density is kept high. Is difficult, and the viscosity of the molten metal is too low,
For this reason, variation in relative density due to defects such as gas defects increases.

Further, the invention of claim 3 of the present application (hereinafter referred to as third invention)
Is a semi-molten injection molding method of a light metal member in which a molten metal is injected and filled into a molding cavity of a mold in a semi-molten state to obtain a molded product, wherein the relative density of the molded product is reduced. Assuming that ρ [%] and the solid phase ratio are α [%], the relationship between them is -2.5 × α + 31 × ρ-2790 ≧ 20.
The molding is performed under the condition satisfying 0.

Further, the invention of claim 4 of the present application (hereinafter referred to as a fourth invention) is characterized in that in the third invention,
Molding is performed under the condition that the relationship between the relative density (ρ [%]) and the solid fraction (α [%]) satisfies −2.5 × α + 31 × ρ-2790 ≧ 230. .

Further, the invention according to claim 5 of the present application is further provided.
(Hereinafter, referred to as a fifth invention) is characterized in that, in any one of the first to fourth inventions, molding is performed with the solid phase ratio α ≧ 10 [%] set.

The reason why the lower limit of the solid fraction (α) is set to 10% is that when the solid fraction is less than 10%, the defect amount is not more than a certain value (specifically, it is generally considered practically preferable). 3% or less), in other words, it is difficult to maintain the relative density at or above a certain level (specifically, at least 97% or more, which is generally preferred for practical use). This is because it is difficult to inject and fill the molding cavity in a state close to the flow, so that the bias of the defect distribution becomes large.

Further, the invention according to claim 6 of the present application is further provided.
(Hereinafter referred to as a sixth invention) is characterized in that, in any one of the first to fifth inventions, a magnesium alloy melt is used as the light metal melt.

[0020]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a partial cross-sectional explanatory view showing a schematic configuration of an injection molding machine that performs injection molding of a light metal member according to the present embodiment. As shown in this figure, the injection molding machine 1 is a so-called screw type, which has a nozzle 3 at a tip end and a heater 4 arranged on the outer periphery.
, A screw 6 rotatably supported in the molding machine main body 5 connected to the cylinder 2 and the cylinder 2, and a rotation driving device that includes, for example, a motor mechanism and a reduction mechanism, and drives the screw 6 to rotate. 7, a hopper 8 into which the raw material is charged and stored, and a feeder 9 for measuring the raw material in the hopper 8 and feeding it into the molding machine main body 5. Although not specifically shown, a high-speed injection mechanism for advancing the screw 6 toward the nozzle 3 is provided in the molding machine main body 5. This high-speed injection mechanism advances the screw 6 at a predetermined timing,
When the screw 6 retreats by a preset distance, it is detected that the rotation of the screw 6 is stopped and the retreat operation is also stopped at the same time.

In the injection molding machine 1, the position of the inner passage of the nozzle 3 and the runner 12 connected to the molding cavity 11 are set so as to communicate with each other. Used. The raw material charged into the hopper 8 and stored therein is measured in a predetermined amount by a feeder 9 and supplied to the molding machine main body 5, and is supplied to the heated cylinder 2 by the rotation of the screw 6. . The fed raw material is screwed inside the cylinder 2
The mixture is heated to a predetermined temperature while being sufficiently stirred and kneaded by the rotation of. In the present embodiment, a metal melt in a semi-molten state (basically lower than the melting point of the raw material) is obtained by such a process.

As the molten metal in the semi-molten state obtained in this way is pushed forward of the screw 6, the screw 6 moves backward by the pressure. As another method, the screw may be forcibly retracted at a desired speed. When the screw 6 retreats by a preset distance, the high-speed injection mechanism (not shown) in the molding machine main body 5 detects this and stops the rotation of the screw 6 and at the same time stops the retreat operation. The measurement of the raw material may be performed by setting the retreat distance of the screw 6.

The screw 6 that has stopped rotating and is in the retracted position is advanced by a high-speed injection mechanism (not shown) and is pushed out by a predetermined force, so that the molten metal in a semi-molten state enters the mold 10 from the nozzle 3. Be injected. That is, the molten metal is injected and filled into the molding cavity 11 from the nozzle 3 through the runner portion 12. In the present embodiment, a magnesium (Δg) alloy, which is a kind of light metal, is used as a raw material, and is supplied to the hopper 8 of the injection molding machine 1 in the form of, for example, swarf pellets. An inert gas (for example, argon gas) is more preferably provided in a passage leading from the hopper 8 into the molding machine body 5.
To prevent the oxidation reaction of the raw material (Mg alloy pellets).

Further, in the present embodiment, when molding a light metal member by the semi-solid injection molding method, the basic purpose is to obtain more stable the desired member strength considered to be practically preferable. Various tests were performed. These tests were conducted on a magnesium alloy {D1 (AST)} containing aluminum specified in JIS H 2222.
B94 AZ91), ΔD shown in Table 1 below
Performed using 1D as raw material. In addition, these three kinds of ΔD1
The alloys (A, B and D) have the same mechanical properties,
The corrosion resistance is different.

[0025]

[Table 1]

In these tests, various molding conditions of semi-solid injection molding (temperature of a molding die, temperature of an injection cylinder or injection speed, and holding pressure during molding) were changed in the following ranges. Molding was performed. -Mold temperature: 100 to 250 [° C]-Cylinder temperature: 570 to 620 [° C]-Injection speed: 0.5 to 3.0 [m / sec.]-Holding pressure: 0 to 100 [МPa]

The relationship between the solid fraction of the molten light metal and the relative density or the tensile strength, or the relationship between the relative density and the tensile strength, was examined by variously changing the molding conditions within the above range. As shown in FIG. 2, the relative density increases with an increase in the solid fraction, but in a region where the solid fraction is low, the variation in the relative density with respect to the same solid fraction is very large. It has been found that this variation decreases as the solid fraction increases.

On the other hand, as shown in FIG. 3, in the case of tensile strength, the higher the solid fraction, the larger the variation. The tensile strength tends to be substantially constant with respect to the change in the solid fraction, or to slightly decrease as the solid fraction increases. Further, when examining the relationship between the relative density and the tensile strength, as shown in FIG. 4, the tensile strength tends to slightly increase as the relative density increases.

In the graph of FIG. 2, the curve showing the lower limit of the variation range of the relative density is represented by the following straight line when the relative density of the molded article is ρ [%] and the solid phase ratio is α [%]. (See the broken line in FIG. 2). .Rho. = 0.1.times..alpha. + 96... Accordingly, semi-solid injection molding is performed in the graph of FIG. 2 so as to fall within the region above this straight line, that is, under the condition of satisfying .rho.≥0.1.times..alpha. + 96. As a result, even if there is a variation in the relative density with respect to the solid fraction, a relative density equal to or greater than a certain value (greater than or equal to the lower limit) can be obtained with respect to a predetermined solid fraction.

In this case, it is preferable to perform molding by setting the solid phase ratio α ≧ 5 [%]. By setting the lower limit value of the solid fraction α to 5%, the absolute amount of coagulation and contraction after injection is reduced accordingly, and the relative density can be kept high. Becomes less likely to be involved, so that it is possible to suppress variations in relative density due to defects such as gas defects.

Further, for the solid fraction α, α ≧ 10
It is more preferable to perform molding by setting to [%]. For the relative density, maintain a value of 97% or more (that is,
It is practically preferable to suppress the defect amount to 3% or less) because the strength decrease is small and it is practically preferable. However, from the test results shown in FIG. 2, by setting the lower limit of the solid fraction (α) to 10%, the defect amount is reduced. To a certain level or less (specifically, 3% or less that is practically preferable), in other words, the relative density can be maintained at a certain level or more (specifically, 97% or more that is practically preferable), Further, it is possible to inject and fill the molten metal into the molding cavity in a state relatively close to laminar flow, so that the deviation of the defect distribution can be reduced.

As can be clearly understood from the graphs of FIGS. 3 and 4, even if the solid fraction is the same and the relative density is the same, a considerable difference (variation) occurs in the tensile strength. Therefore, it is generally preferable that a light metal member such as a Мg alloy member has a tensile strength of about 200 МPa or more for practical use. In addition, in the case of the Al-containing Мg alloy МD1 used in this test, the JIS reference value is used. 230МP as
The tensile strength of a is indicated, and it is said that it is more preferable to have a higher strength. However, when these strengths are to be ensured by the semi-solid injection molding method, only the solid fraction or the relative density Even if only the value is set to be equal to or more than a certain value, the desired tensile strength cannot be obtained stably.

In this embodiment, a specific parameter (Psd) expressed by the following equation, which is a combination of the solid fraction (α) and the relative density (ρ), is adopted. The interphase relation was examined. The result is shown in FIG. Parameter: Psd = −2.5 × α + 31 × ρ-279
0 As shown in FIG. 5, this parameter Psd (−2.5 × α
+ 31 × ρ-2790) and the tensile strength of the molded product are significantly higher than those shown in FIG. 3 (solid fraction and tensile strength) or FIG. 4 (relative density and tensile strength). It turned out that there was. That is, as can be clearly understood from the graph of FIG. 5, if the data is arranged by taking the tensile strength on the vertical axis Y and the parameter Psd on the horizontal axis X, each data point becomes a straight line represented by the following equation. Approximately at the center, it is distributed within a fairly narrow range.・ Y = X ...

Accordingly, the desired tensile strength can be stably obtained by setting and molding the conditions based on the straight line in the graph of FIG. That is, 2
To obtain a tensile strength of 00 ° Pa or more, Y
= X ≧ 200, and molding may be performed under the conditions satisfying the following expression. Parameter: Psd = −2.5 × α + 31 × ρ−2790 ≧ 200 By forming under these conditions, a tensile strength of about 200 ° Pa or more, which is considered to be practically preferable to be provided as a light metal member such as a Δg alloy member. Strength can be more stably secured.

When it is desired to obtain a tensile strength of 230 ° Pa or more, it is sufficient that Y = X ≧ 230 and molding is performed under the conditions satisfying the following equation. Parameter: Psd = −2.5 × α + 31 × ρ−2790 ≧ 230 By forming under such conditions, it is more preferable to provide as a light metal member such as a Δg alloy member. ２2, which is the JIS reference value for D1
It is possible to more stably secure a tensile strength of 30 ° Pa, and it can be applied to a relatively high load, for example, a mechanical component. As described above, according to the present embodiment, when molding a light metal member by the semi-solid injection molding method, the desired member strength can be obtained more stably.

The present invention is not limited to the above-described embodiment, but may be modified without departing from the scope of the invention.
It goes without saying that various improvements or design changes are possible.

[0037]

According to the first aspect of the present invention, when a light metal melt is injected into a molding cavity of a mold in a semi-molten state to obtain a molded product, the relative density of the molded product is set to ρ.
[%] And the solid fraction is α [%], the relationship between the two is ρ ≧
Since the molding is performed under the condition satisfying 0.1 × α + 96, even if there is a variation in the relative density with respect to the solid phase ratio,
With respect to a predetermined solid fraction, a relative density equal to or more than a certain value (not less than a lower limit) can be obtained.

According to the second aspect of the present invention, basically, the same effects as those of the first aspect can be obtained. In particular, since the molding is performed with the solid phase ratio α ≧ 5 [%], the absolute amount of solidification shrinkage itself after injection is reduced accordingly, and the relative density can be kept high.
In addition, the viscosity of the molten metal is also maintained at a high level, making it difficult for the gas to be entrained. For this reason, it is possible to suppress variations in relative density due to defects such as gas defects.

Further, according to the third aspect of the present invention, when a light metal melt is injected and filled in a semi-molten state into a molding cavity of a molding die to obtain a molded product, the relative density of the molded product is set to ρ [%]. , The solid phase ratio is α [%], and the relationship between the two is −
Since molding is performed under the condition of 2.5 × α + 31 × ρ-2790 ≧ 200, it is relatively stable to secure a tensile strength of about 200 ° Pa or more, which is considered to be practically preferable to be provided as a light alloy member. can do.

Further, according to the fourth invention of the present application,
Basically, the same effects as in the third aspect can be obtained. In particular, the relationship between the relative density ρ and the solid fraction α
Since the molding is performed under the condition of −2.5 × α + 31 × ρ−2790 ≧ 230, the tensile strength of about 230 ° Pa or more, which is more preferably provided as a light alloy member, is relatively stably secured. be able to.

Further, according to the fifth invention of the present application,
Basically, the same effect as any one of the first to fourth inventions can be obtained. In particular, the solid fraction α ≧ 10
[%], The molding is performed so that the defect amount is suppressed to a certain value or less (specifically, 3% or less, which is practically preferable), in other words, the relative density is set to a certain value or more (specifically, Is 97% or more, which is practically preferable), and the molten metal can be injected and filled into the molding cavity in a state relatively close to laminar flow, so that the bias of the defect distribution can be reduced. .

Further, according to the sixth invention of the present application,
Since the melt of the Мg alloy is used as the light metal melt, when the Мg alloy member is semi-solid injection molded,
The same effect as any one of the first to fifth inventions can be obtained.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional explanatory view showing a schematic configuration of an injection molding apparatus according to an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a solid phase ratio and a relative density of the light metal member according to the embodiment of the present invention.

FIG. 3 is a graph showing a relationship between a solid fraction and a tensile strength of the light metal member.

FIG. 4 is a graph showing a relationship between a relative density and a tensile strength of the light metal member.

FIG. 5 is a graph showing a relationship between a relative density of the light metal member and a parameter according to the present embodiment.

[Explanation of symbols]

 10: Mold 11: Mold cavity

Claims (6)

[Claims] 1. A semi-solid injection molding method for a light metal member, wherein a light metal melt is injected and filled in a molding cavity of a mold in a semi-molten state to obtain a molded product, wherein a relative density of the molded product is ρ A semi-solid injection molding method for a light metal member, characterized in that molding is performed under the condition that the relationship between the two satisfies ρ ≧ 0.1 × α + 96, where [%] and the solid phase ratio are α [%]. 2. The semi-solid injection molding method for a light metal member according to claim 1, wherein the molding is performed with the solid phase ratio α ≧ 5 [%]. 3. A semi-solid injection molding method for a light metal member, wherein a light metal melt is injected and filled in a semi-molten state into a molding cavity of a molding die to obtain a molded product, wherein the relative density of the molded product is ρ [%] And the solid fraction as α [%], the relationship between the two is -2.5 × α + 31 × ρ-279.
A semi-solid injection molding method for a light metal member, characterized in that molding is performed under conditions satisfying 0 ≧ 200. 4. The relative density (ρ [%]) and the solid fraction (α
[%]) Is -2.5 × α + 31 × ρ-2790.
The method for semi-solid injection molding of a light metal member according to claim 3, wherein the molding is performed under a condition satisfying ≧ 230. 5. The semi-solid injection molding method for a light metal member according to claim 1, wherein the molding is performed with the solid phase ratio α ≧ 10 [%]. 6. The semi-solid injection molding method for a light metal member according to claim 1, wherein a molten metal of a magnesium alloy is used as the molten light metal.