JPH081305A - Method for pressure-casting molded product dispersed reinforcing material - Google Patents

Abstract

PURPOSE:To surely and easily obtain a high quality cast product by mutually and periodically applying pressurizing forces composed of high pressure and low pressure to molten metal at the interval of a short time. CONSTITUTION:The molten metal 8 is filled up into a cavity 6 in the dies 2, 3. The molten metal 8 is made by mixing reinforcing materials of ceramic fibers, whiskers, particles, etc. The molten metal 8 in the cavity 6 is pressurized with a hydraulic cylinder 10. Oil pressures of the hydraulic cylinder 10 are applied by controlling so as to mutually and periodically act a prescribed high pressure and a prescribed comparatively low pressure at the interval of the short time by a feedback control part 20. In such a way, the pressurizing forces composed of the prescribed high pressure and low pressure mutually and periodically applied to the molten metal 8 solidified in the cavity 6 at the interval of the short time. By this method, the reinforcing materials are made to the form uniformly dispersed, and the strength can be uniformized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method of mixing a reinforcing material of a light metal alloy such as an aluminum alloy or a magnesium alloy with particles of ceramics typified by SiC, short fibers and whiskers as a reinforcing material. The present invention relates to a pressure casting method for casting a mixed molten metal using a mold.

[0002]

2. Description of the Related Art Conventionally, a composite material product in which ceramic particles, short fibers, whiskers, etc. are reinforced is manufactured by a powder metallurgy method, an atomizing method, a casting method, etc. A predetermined product was obtained by performing processing or cutting the product shape as it was.
However, it is extremely difficult to cut a composite material containing a hard reinforcing material such as ceramics, and it is desired to form a net shape. As a technology to meet this demand,
In high-pressure casting machines represented by die casting machines, a casting method of injecting and molding a molten metal in which a reinforcing material is mixed and stirred is being used.

[0003]

In the conventional composite material product manufactured by the high-pressure casting method, since the secondary processing is not performed, the dispersion state of the reinforcing material is determined by the crystal nucleation and crystal growth behavior in the solidification process of the matrix alloy. . Generally, the reinforcing material is extruded into the residual liquid phase between the crystal grains during the solid phase growth without being taken in at the solid / liquid interface. Therefore, in order to obtain the uniform dispersion of the reinforcing material required for the composite material having good mechanical properties, it is desirable that the crystal grains are fine equiaxed crystals. In the simple high-pressure casting method, coarse columnar crystals often grow in the solidification process, and a composite material product in which the reinforcing material is uniformly dispersed in that portion cannot be obtained.

[0004]

In the present invention, in order to solve such problems and obtain the intended effect, the metal pressing force is controlled. That is, a reinforcing material such as ceramic fibers, whiskers or particles is mixed with the molten metal for casting, the molten metal mixed with the reinforcing material is filled into the cavity of the mold, and then a pressing force is applied to the molten metal in the cavity. Cavity is controlled by applying hydraulic pressure to the hydraulic cylinder so that a predetermined high pressure and a predetermined low pressure, which is relatively smaller than this high pressure, are alternately and periodically applied at short time intervals. A metal pressing force consisting of a predetermined high pressure and a predetermined low pressure, which is relatively small compared to the high pressure, is alternately and periodically applied to the solidified molten metal in which the reinforcing material is mixed at short intervals. I did it. In addition, it is desirable to control by feedback control so that the pressure fluctuation width and the pressure fluctuation frequency of the metal pressing force become the intended values.

[0005]

In the present invention, by periodically applying a high pressure and a low pressure to the molten metal in the cavity, the pressure at which the molten metal is pressed against the mold surface changes periodically. In general,
The heat transfer coefficient between the molten metal and the surface of the mold takes a larger value as the pressing pressure increases, and it becomes possible to remove a large amount of heat from the molten metal in a short time. Therefore, if the pressure is changed periodically, the amount of heat removed to the mold will be changed periodically.

Considering the solidification morphology in the case where the amount of heat removed from the mold fluctuates cyclically in this way, it is as follows. That is, under the action of high pressure, the amount of heat of the molten metal in the vicinity of the die surface is rapidly removed, and solidification progresses remarkably instantaneously. And, due to this rapid solid-phase growth, a very large latent heat is released. In ordinary high-pressure casting, since a high pressure is continuously applied, a large amount of heat can be continuously removed to the mold, and the latent heat released during solidification is quickly removed to the mold.

However, when the pressure is changed cyclically as in the present invention, under the action of low pressure, the large amount of latent heat released during the action of high pressure cannot be sufficiently released to the die, and the die surface The molten metal in the vicinity partially rises. Due to such recalescence in the vicinity of the mold (temperature increase due to re-radiation heat and latent heat release), crystal release and fusing release of dendrite branches occur. Further, due to the pressure applied disruptively, the molten metal and the mixed reinforcing material flow, and together with this, crystal release and fusing release of dendrite branches are promoted.

Reinforcing agents such as ceramic particles, short fibers, and whiskers are generally extruded into the residual liquid phase between crystal particles without being taken in at the solid / liquid interface during solid phase growth. In the high-pressure casting method, since high pressure is continuously applied, latent heat is quickly released to the mold, and it is extremely unlikely that crystal liberation and fusing desorption of dendrite branches occur, and often coarse columnar crystal growth occurs. To be observed. In this case, most of the reinforcing material is distributed among the coarse columnar crystals, and it is not possible to obtain an ideal uniform dispersion state in terms of mechanical properties.

However, when high pressure and low pressure are cyclically applied to the molten metal in the cavity as in the present invention, the liberation of crystals and the fusing and liberation of branches of dendrites are remarkably promoted. The organization is obtained. Even in this case, most of the reinforcing material will be distributed among the crystal grains, but the crystal grains themselves are finer than those obtained by the conventional high pressure casting method.
A much more uniform dispersion of reinforcement can be obtained.

[0010]

FIG. 1 shows an apparatus for carrying out the method according to the invention.
It is a longitudinal section showing an example. The casting apparatus main body 1 shown in FIG. 1 is called a horizontal type vertical casting die casting machine, 2 is a fixed die, 3 is a movable die, 4 is a casting sleeve, 5 is a plunger tip, Reference numeral 6 is a cavity, 7 is a gate portion, 8 is a molten metal such as aluminum or magnesium alloy mixed with a reinforcing material such as ceramic fibers, whiskers or particles. In the figure, the molten metal is cast in the direction of the arrow, and the casting pressure is also set. To act.

A pressure block 9 is slidably provided on a part of the movable mold 3 facing the cavity 6,
The piston rod 11 of the hydraulic cylinder 10 was connected to the hydraulic cylinder 10, and the servo valve 12 was connected to the hydraulic cylinder 10. In the supply pressure setting fluctuation device 13, the servo valve 12
The pressure of the hydraulic oil is controlled by controlling the opening of the hydraulic cylinder, and the hydraulic pressure applied to the hydraulic cylinder 10 is controlled.

Reference numeral 14 is a pump, 15 is a motor, 16 is a relief valve for loading and unloading, 17 is a tank, 1
Reference numeral 8 denotes a command device that issues commands for loading and unloading to the relief valve 16 in accordance with opening / closing operations of the machine body, start / end operations of casting, and the like. Pressure casting is performed while controlling the hydraulic pressure of the hydraulic cylinder 10, and accordingly, the hydraulic pressures of the rod side and the head side of the hydraulic cylinder 10 are continuously detected, and feedback control is performed based on that.
Control is performed so that a predetermined changing metal pressure is obtained.

Reference numeral 20 is a feedback control unit, 21 is a pressure model unit, and the pressure model unit 21 has a cavity 6
A metal pressing force consisting of a predetermined high pressure and a predetermined low pressure which is relatively small compared to the high pressure is alternately and periodically applied to the molten metal 8 in which the solidified reinforcing material is dispersed at short intervals. High pressure, low pressure, pressure fluctuation width consisting of an intended constant value, and pressure fluctuation frequency for applying
It is set as a metal pressure diagram or as a numerical value, and an output signal p corresponding to it is output. Of course, for the purpose of controlling the pressure fluctuation frequency and the pressure fluctuation width so as to change according to the passage of the pressurization time, a time-metal pressure diagram or the like may be set.

Reference numeral 22 is a pressure deviation detector, which compares the output signal p from the pressure model section 21 with the output signal from the pressurization pressure calculator 23, detects the deviation, and outputs an output signal corresponding to the deviation value. e is output to the gain setting unit 24.

The pressure on the head side of the hydraulic cylinder 10 is detected by the pressure detecting device 25, and the value thereof is input as a signal to the pressurizing pressure calculator 23 via the amplifier 26 and the analog / digital converter 27. On the other hand, hydraulic cylinder 1
The pressure on the rod side of 0 is the pressure detection device 28, the amplifier 29,
It is input as an input signal to the pressurization pressure calculator 23 via the analog-digital converter 30.

In the pressurizing pressure calculator 23, the bore sectional area of the hydraulic cylinder 10 is A, the sectional area of the piston rod 11 is a, the pressing sectional area of the pressurizing block 9 is S, the head side pressure is P ₁ , the rod-side pressure P _2, when the pressure generated pressure block 9 and the _{P 0, P 0 = (1} / S) × _{[a · P 1 - (a-} a) · P 2 ] as the pressure P ₀ Is calculated, and the output signal corresponding to this value is input to the pressure deviation detector 22 as described above.

In the gain setting section 24, the pressure deviation detector 2
The input / output signal e from 2 is input, the corrected output signal v is output to the driver 31, and the driver 31 outputs the output signal i.
Output to the solenoid 12a of the servo valve 12. Then, according to the action of the servo valve 12, the hydraulic cylinder 1
The hydraulic pressure of 0 is controlled appropriately.

When the metal pressure is to be obtained, as described above, instead of detecting the oil pressure of the hydraulic cylinder 10, it is measured by the pressure sensor installed in the molds 12, 13.
It can also be calculated based on the value. Further, the dies 12, 13 which are in direct contact with the molten metal 8 in the cavity 6
It is also possible to move forward a movable member provided so as to project on a part of the mold or a part of the molds 12 and 13 thereof by controlling the hydraulic pressure of the hydraulic cylinder.

In the apparatus shown in FIG. 1, first, the plunge
Due to the forward action of the chip 5, the reinforcing material composed of SiC particles
For example, 6061 aluminum mixed with a volume content of 20%
The molten metal 8 of the aluminum alloy to the molds 2 and 3 at a mold temperature of 200 ° C.
The molten metal is cast in the vity 6 at a temperature of 750 ° C. and filled,
800 kg / cm, for example, in the molten metal 8 with the Langer chip 5 ² 
High pressure of.

When the molten metal 8 is filled in the cavity 6,
Immediately actuate hydraulic cylinder 10 to mix reinforcement
For example, 700 plus or minus 100 kg /
cm ² Of metal pressure, that is, high pressure is 800k
g / cm² , Low pressure is 600kg / cm² Metal pressure
Alternating forces in pulses, eg at 100 Hz
As shown in FIG.
By the feedback control described above, for example, 20 seconds
As described above, the pulses are alternately operated for a predetermined time. Melting
When the hot water 8 has cooled and solidified, the mold is opened and the cast product is taken out.
You.

The structure of the cast product thus obtained is shown in FIG. From FIG. 2, it can be seen that fine equiaxed crystals 32 are formed up to the surface of the cast product, that is, the entire surface. In FIG. 2, 33 is SiC particles as a reinforcing material, and 35 is a product end surface. When the metal pressure is applied in a pulsed manner, the change state of the structure in the molten metal 8 in which the reinforcing material is mixed in the portion near the mold surface changes as follows. First, when the high pressure is applied for the first time, the molten metal 8 is strongly pressed against the surfaces of the molds 2 and 3, and crystals start to form.

Next, if a relatively low pressure is applied,
The force by which the molten metal 8 is pressed against the surfaces of the molds 2 and 3 becomes weaker by that amount, and the degree of heat transfer from the molten metal 8 to the molds 2 and 3 also becomes smaller accordingly. Happens. Therefore, even if a high pressure is applied next, the crystal remains fused and remains free, and these become nuclei, and solidification proceeds. As a result, columnar crystals do not occur due to rapid repetition of high pressure and low pressure, and fine equiaxed crystals 32 are formed on the entire surface. Then, segregation is prevented, hot cracking is prevented, and strength is improved by refining crystal grains. In addition,
In this case, most of the reinforcing material is distributed among the crystal grains, but since the crystal grains themselves are fine, the reinforcing material is uniformly dispersed.

On the other hand, in the conventional method, when the molten metal 8 mixed with the reinforcing material is continuously cast by applying a constant metal pressure of 800 kg / cm ² for 20 seconds, the obtained cast product is obtained. The organization of Fig. 3 appeared as shown in Fig. 3. In FIG. 3, columnar crystals 34 appear on the surface and equiaxed crystals 32 appear inside. In addition, alloy composition, pouring temperature, mold temperature, used molds 2, 3 etc.
The conditions were the same as when the metal pressure was applied in a pulsed manner.

Looking at the change state of the structure in the molten metal 8 mixed with the reinforcing material in the portion close to the mold surface when a constant pressure is applied, the heat transfer from the molten metal 8 to the molds 2, 3 is observed. Is still large, segregation occurs, and columnar crystals 34 appear on the entire surface of the cast product.

When carrying out the present invention, the type of alloy to be cast as a molten metal mixed with a reinforcing material, the shape and dimensions of the cast product,
Depending on the casting conditions, the best high metal pressure,
Low pressure, pressure fluctuation amplitude, pressure fluctuation frequency, etc. are somewhat different. However, it is necessary that the pressure fluctuation amplitude of the metal pressure applied in a wavy manner exceeds a certain value.
We know from the experimental results so far.

For example, the molten metal mixed with the reinforcing material is 7 ××
For alloys with few solute elements and columnar crystals that are likely to grow, such as x-type alloys, a pressure fluctuation range of plus or minus 100 kg / cm ² or more is required, and as in the case of AC7A, AZ91, etc. Regarding alloys that are easily generated, for example, in AZ91, plus or minus 40 kg /
cm ² or so, in AC7A, plus or minus 20kg /
A pressure fluctuation range of about cm ² is effective. However, AZ9
For alloys whose solid phase high temperature strength is extremely low, such as 1), excessive pressure fluctuations, for example, in the case of AZ91, when pressure fluctuations of plus or minus 100 kg / cm ² or more are applied, conversely hot cracking occurs. It is easy to cause
As described above, when the pressure is applied to the molten metal in a wavy manner, it is necessary to control the fluctuation range of the pressure so as to be an appropriate value based on experience and experimental results.

According to our experimental results, if the fluctuation range of the metal pressing force is not more than plus or minus 10 kg / cm ² , even the alloys which are originally prone to equiaxed crystals such as AC7A and AZ91 are completely effective. It is not allowed. In order to reliably obtain the effect, 20 kg / cm ² or more is necessary even for an alloy such as AC7A which is likely to form equiaxed crystals. Of course, the upper limit of the fluctuation range of the metal pressure is such that hot cracking does not occur depending on the high temperature strength of each alloy,
For example, with AZ91, plus or minus 100 kg / c
Must be decided for each alloy, such as m ² or less. The average pressure is 200 kg / cm ²
The above is required, but 400 is required for cast products that are susceptible to shrinkage cavities.
It is preferably at least kg / cm ² .

Regarding the pressure fluctuation frequency, no effect is recognized at 0.5 Hz or less. Originally, in alloys that tend to form equiaxed crystals, the effect is observed at 2 Hz or higher,
To surely obtain the effect, 5 Hz or higher is preferable. Further, a frequency of 1000 Hz or higher is not necessary, and some effects have been recognized in all the alloys tested so far as long as the frequency is up to 500 Hz. However, in order to realize the frequency of 500 Hz, the pressurizing device has a large capacity, and there is a problem in terms of cost. Generally, a frequency of 200 Hz or less is sufficient. Under such preferable conditions, segregation does not occur, crystal liberation and fusing of dendrites are promoted, fine equiaxed grains are formed on the entire surface of the cast product, quality improvement is performed, and heat No cracks or shrinkage cavities occur.

[0029]

As described above, according to the present invention, as described in the scope of claims, the molten metal for casting in which the reinforcing material is mixed is filled in the cavity of the die, and the molten metal in the cavity is pressed. Cavity is controlled by applying hydraulic pressure to the hydraulic cylinder to which a predetermined high pressure and a predetermined low pressure that is relatively small compared to this high pressure are alternately and periodically applied at short intervals. Control is performed by periodically and alternately applying to the solidified molten metal in a predetermined high pressure and a predetermined low pressure, which is relatively small compared to this high pressure, alternately at short intervals. For example, since the fluctuation width and fluctuation frequency of the metal pressure force are controlled by feedback control so that they are at the intended values, when a relatively low pressure is applied immediately after a high pressure is applied, the metal pressure is temporarily reduced. Mold surface heat Reaches coefficient decreases, 潛熱 that occurred during solidification is not sufficiently heat removal from the mold surface, it increased melt temperature partially crystalline free and dendritic blown free of branches of crystals occurs. Further, due to the pressure of a necessary and sufficient value that is applied in a wavy manner, the molten metal flows, which is also combined to promote crystal release and fusing release of dendrite branches.

As a result, columnar crystals are not formed, only equiaxed zones are formed on the entire inner surface of the cast product, and solute elements are not segregated in the equiaxed zones. Therefore, hot cracking does not occur, shrinkage cavities hardly occur, and a high-quality cast product with high strength and toughness can be reliably and easily obtained. Most of the reinforcements are distributed among the crystal grains, but the crystal grains themselves are fine, so the reinforcements are uniformly dispersed and the strength is constant.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of an apparatus for carrying out the present invention.

FIG. 2 is a structural diagram of a cast product obtained according to the present invention.

FIG. 3 is a structural diagram of a cast product obtained by a conventional method.

[Explanation of symbols]

 1 Casting Device Main Body 2 Fixed Die 3 Movable Die 4 Casting Sleeve 5 Plunger Chip 6 Cavity 8 Molten Metal Mixing Reinforcement 9 Pressurizing Block 10 Hydraulic Cylinder 12 Servo Valve 13 Supply Pressure Setting Fluctuation Device 20 Feedback Control Unit 21 Pressure Model part 22 Pressure deviation detection part 23 Pressurized pressure calculator 24 Gain setting part 25, 28 Pressure detection device 31 Driver 32 Equiaxed crystal 33 SiC particle (reinforcing material) 34 Columnar crystal

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B22D 18/02 L 27/09 A

Claims (8)

[Claims] 1. A molten metal for casting is mixed with a reinforcing material such as ceramic fibers, whiskers or particles, and the molten metal mixed with the reinforcing material is filled in a cavity of a mold and then added to the molten metal in the cavity. Applying hydraulic pressure to a hydraulic cylinder that applies pressure by controlling so that a predetermined high pressure and a predetermined low pressure that is relatively small compared to this high pressure are alternately and periodically applied at short time intervals. With this, the metal pressure consisting of a predetermined high pressure and a predetermined low pressure, which is relatively small compared to this high pressure, is alternately applied to the solidified molten metal in which the reinforcing material is mixed in the cavity at short intervals. Method for pressure-molding a molded product in which a reinforcing material that has been added selectively is dispersed. 2. The pressure casting method according to claim 1,
Reinforcement in which a high pressure and a relatively low pressure, which is relatively small compared to this high pressure, are controlled and added with the intended pressure fluctuation width and pressure fluctuation frequency to the solidified molten metal in which the reinforcing material in the cavity is mixed A method of pressure casting a molded product in which a material is dispersed. 3. The pressure casting method according to claim 2,
Set when adding a high pressure and a relatively low pressure that is relatively small compared to this high pressure to the mixed solidified molten metal of the reinforcing material in the cavity by controlling with the intended pressure fluctuation width and pressure fluctuation frequency. A pressure casting method for a molded article in which a reinforcing material is dispersed, which is controlled by feedback control based on pressure and measured pressure. 4. The pressure casting method according to claim 3,
The trajectory of the metal pressure force set in advance with a predetermined pressure fluctuation width and pressure fluctuation frequency, and the hydraulic pressure on the rod side and head side of the hydraulic cylinder were measured with a pressure sensor and calculated based on these values. The oil pressure applied to the hydraulic cylinder is properly controlled according to the amount of deviation from the metal pressure or the metal pressure measured by the pressure sensor installed in the mold, and the metal pressure is a preset pressure locus. A method for pressure-casting a molded product in which a reinforcing material is dispersed so as to follow the above. 5. The pressure casting method according to claim 1,
When a pressure is applied to the molten metal in the cavity, a part of the mold that is in direct contact with the molten metal in the cavity or a movable member that can be projected on the part of the mold is used to increase the oil pressure of the hydraulic cylinder. A method for pressure-casting a molded article in which a reinforcing material is dispersed so as to be advanced by controlling. 6. The pressure casting method according to claim 1,
A pressure casting method for a molded article in which a reinforcing material is dispersed, in which a metal pressure having a pressure fluctuation range of plus or minus 10 kg / cm ² or more is applied to a molten metal. 7. The pressure casting method according to claim 1,
Average pressure of 200 kg / cm ² or more and plus or minus 1
A method for pressure casting a molded product in which a reinforcing material is dispersed, which is made to act on a molten metal with a pressure fluctuation width of 0 kg / cm ² or more and a pressure fluctuation frequency of ² to 500 Hz. 8. The pressure casting method according to claim 1,
Average pressure of 400 kg / cm ² or more and plus or minus 2
A method for pressure casting a molded product in which a reinforcing material is dispersed, which is made to act on a molten metal with a pressure fluctuation width of 0 kg / cm ² or more and a pressure fluctuation frequency of 5 to 200 Hz.