JPH1015654A - Method for casting cast product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a casting method which can obtain a casting excellent in the casting precision without needing specially high toughness of a metallic mold and a casting machine, etc. SOLUTION: Molten metal 10 is filled into a cavity 5 formed in the metallic mold 1 under the atmosphere (casting process). After this casting process, the molten metal is solidified by pressing according to the degree of solidification of the molten metal in the cavity 5 of the metallic mold 1 (pressing process). In the pressing process, at the time of starting the solidification of the molten metal 10 near the surface of the cavity 5 in the metallic mold 1, the molten metal 10 is pressed at 2-5kg/cm<2> press, and at the time of starting the solidification of the molten metal in the cavity 5 forming a thick part of the casting in the condition of holding this state, the molten metal 10 is pressed at 10-25kg/cm<2> pressure. The press of the molten metal is executed by inserting piston rods 21, 22 in the pressing device 15 into a feeder head 14 of the molten metal 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for casting a good casting which is applied to the manufacture of a piston for an internal combustion engine and the like.

[0002]

2. Description of the Related Art In recent years, in order to improve efficiency, an internal combustion engine of a type in which fuel is directly injected into a cylinder has been developed. In this internal combustion engine, a piston having an uneven top surface is employed. The piston is formed by a pressure casting method in order to accurately cast the uneven shape of the top surface.

The above pressure casting method is disclosed in, for example,
As disclosed in Japanese Patent No. 0266, molten metal (molten metal) is placed in a mold having a cavity formed therein at a pressure higher than atmospheric pressure.
And then applying a higher pressure to solidify the molten metal under pressure to obtain a product.

[0004]

However, in the above conventional example, the molten metal is filled while applying pressure,
Since pressure is applied at a high pressure of 30 kg / cm2 or more, not only the rigidity of the mold needs to be increased, but also the rigidity of the entire casting machine needs to be increased.
It may be expensive.

The present invention has been devised in view of the above-mentioned conventional circumstances, and does not require a particularly high rigidity of a mold, a casting machine, and the like, and a casting method capable of obtaining a casting with excellent casting accuracy. The purpose is to provide.

[0006]

Accordingly, the present invention is directed to a casting step of filling a cavity formed in a mold with a molten metal at atmospheric pressure, and, after the casting step, a step of filling the mold with the molten metal. A pressurizing step of pressurizing the inside of the cavity in accordance with the degree of solidification of the molten metal to solidify the molten metal.

According to a second aspect of the present invention, in the configuration of the first aspect, the step of pressurizing the molten metal is performed when the molten metal near the cavity surface of the mold starts to solidify.
A first stage of pressurizing at a pressure of 5 kg / cm2, and then
When the molten metal in the cavity forming the thick part of the casting starts to solidify, a second stage of applying a pressure of 10 to 25 kg / cm @ 2 is provided.

According to a third aspect of the present invention, in the configuration of the first or second aspect, the step of pressurizing the molten metal is performed by a piston rod inserted into a riser of the molten metal. It is.

According to a fourth aspect of the present invention, in the configuration of the first or second aspect of the invention, the step of pressurizing the molten metal is performed by air pressure acting on a riser of the molten metal. is there.

According to a fifth aspect of the present invention, in the first to fourth aspects of the present invention, the mold having the cavity has an upper mold and a lower mold having a gate. The upper die is made of a sintered metal material.

Here, in the casting step, the filling of the molten metal (molten metal) into the cavity formed in the mold is performed under atmospheric pressure, and no special pressurization is performed. That is, an ordinary so-called gravity casting method is adopted, and the force given to the molten metal filled in the cavity is given only by the gravity acting on the molten metal in the gate located above the cavity.

The pressing step after the casting step can be performed by applying a predetermined pressure to the feeder.
In the invention described in claim 4, the air for pressurizing the core of the molten metal includes various inert gases and the like in addition to the atmosphere.

The start of the pressurizing step is when the molten metal near the cavity surface of the mold has started to solidify, and the start timing is when an extremely thin solidified layer is formed near the cavity surface or the solidification occurs. It is a so-called porosity solidification in which a layer is not formed, and a state of a solid-liquid coexisting phase is preferable.
(On the order of seconds). The same applies to the pressurization start timing of each stage when the pressurization step is made into two stages in the invention according to the second aspect. When the molten metal in the cavity that forms the part begins to solidify, an extremely thin solidified layer is formed near the surface of the cavity or in a solid-liquid coexisting phase, which is also the time elapsed from the reference time. Can be determined by

In the pressurizing step, after the pressurization is started, a high pressure is applied according to the degree of solidification of the molten metal. The pressure according to the degree of solidification of the molten metal does not need to be gradually increased according to the degree of solidification of the molten metal, and can be increased by a stepwise increasing pressure.

Therefore, since the pressurizing step is performed at a pressure corresponding to the degree of solidification of the molten metal, that is, when most of the molten metal is in a liquid phase, it is pressurized at a relatively low pressure, and the molten metal is pressurized at a high pressure. When pressurized, part of the molten metal is solidified particularly near the cavity surface of the mold, so that it is not necessary to increase the rigidity of the mold and the casting machine, etc. Obtainable.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings as embodiments applied to a method of casting a piston for an internal combustion engine.

FIG. 1 is a schematic sectional view showing an apparatus for applying an embodiment of the present invention to a method for casting a piston for an internal combustion engine, and FIG. 2 is a sectional view taken along line AA of FIG. 1 in the figure
Is a mold, and the mold 1 has an upper mold 2, a lower mold 3, and a core 4. In the mold 1, a cavity 5 of a piston for an internal combustion engine (hereinafter, referred to as a piston) as a casting material is formed. Reference numeral 6 denotes a ring mold disposed between the upper mold 2 and the lower mold 3. Reference numeral 7 denotes a pin core forming a pin hole portion of the piston, and the tip of the pin core 7 projects from the lower mold 3 into the cavity 5.

The upper die 2 is shaped so as to form a crown portion of a piston. The upper die 2 is made of a heat-resistant powder of stainless steel or die steel and has pores having a diameter of about 20 μm. It is sintered into a shape. In this embodiment, the surface of the upper mold 2 forming the cavity 5 is not coated with diatomaceous earth or the like.

A gate 8 communicating with the cavity 5 is formed in the lower mold 3. The gate 8 is a ladle 9
Funnel-shaped pool 11 for receiving molten metal 10 from the like, a vertical gate 12 communicating with the pool 11, and a vertical gate 12
And a runner 13 communicating with the inside of the cavity 5 and a weir (not shown). The basin 11 of the gate 8 is disposed above the cavity 5 as in the case of ordinary gravity casting. Further, a piston (cast) is provided in the lower mold 3.
Facing the cavity 5 forming the thick part of the feeder 14
Is formed.

Reference numeral 15 denotes a pressurizing device. This pressurizing device 15
Is a slider 17 slidably provided on a gantry 16.
And the first cylinder device 1 for sliding the slider 17
8 and a second cylinder device 19 fixed to the slider 17.

The first cylinder device 18 is mounted on a gantry 16. The first cylinder device 18 includes a rod 20 that can move forward and backward, and the rod 20 is connected to the slider 17. Therefore, the first cylinder device 18 can move the slider 17 by the reciprocating operation of the rod 20.

The second cylinder device 19 includes a rod 21 that moves forward and backward and a guide cylinder 22 that guides the rod 21.
The guide tube 22 extends through the side plate 23 of the mold 1 while enclosing the rod 21 and extends into the mold 1. The rod 21 can move forward and backward with respect to the second cylinder device 19, but the guide cylinder 22 is integrally fixed to the second cylinder device.

In the normal state, the rod 21 and the guide cylinder 22 of the second cylinder device 19 have their tips 21a, 22a at their ends 21a, 22a as shown in FIG. When the first cylinder device 18 and the second cylinder device 19 are operated, the molten metal 10 can be inserted into the feeder 14. Accordingly, the rod 21 and the guide cylinder 22 are used to hold the feeder 1 of the molten metal 10.
4 will function as a piston rod to be inserted.

In the apparatus having such a configuration, the molten metal 10 is poured into the gate 8 from the ladle 9 or the like, and is filled in the cavity 5 of the mold 1 (casting step). The filling of the molten metal 10 into the cavity 5, that is, the casting step is performed under atmospheric pressure. Therefore, the molten metal 10 filled in the cavity 5
Is applied only by gravity acting on the molten metal in the gate 8 located above the cavity 5.

Next, after the casting step, the inside of the cavity 5 of the mold 1 is pressurized according to the degree of solidification of the molten metal to solidify the molten metal (pressing step). This pressurizing step is as follows in this embodiment.

First, as a first step, when the molten metal 10 near the surface of the cavity 5 of the mold 1 starts to solidify, the molten metal 10 is pressurized at a pressure of 2 to 5 kg / cm 2. The first stage pressurization start time is a time when a very thin solidified layer is formed in the vicinity of the surface of the cavity 5 or a so-called porridge solidification in which a solidified layer cannot be formed, in a state of a solid-liquid coexisting phase. Is started about 5 seconds after the completion of the casting step. In the first stage pressurization, the first cylinder device 18 of the pressurizing device 15 is operated, and the slider 17 is moved to the second cylinder device 1.
9, the rod 21 and the guide cylinder 22 of the second cylinder device 19 are inserted into the riser 14 of the molten metal 10 (see FIG. 3). The pressurizing speed in this case is a slow speed of about 1 cm / sec.

Next, as a second stage, when the molten metal in the cavity 5 forming the thick part of the piston (casting) starts to solidify while maintaining the pressurized state of the first stage, the molten metal 10 At a pressure of 10 to 25 kg / cm @ 2. The pressurization start time in the second stage is a so-called porosity solidification in which an extremely thin solidified layer is formed in the vicinity of the surface of the cavity 5 forming the thick part of the piston (casting) or the solidified layer is not formed. In the state of the liquid coexistence phase, specifically, it is started within about 10 seconds after the first stage pressurization. The second stage pressurization is performed by operating the second cylinder device 19 of the pressurizing device 15 and inserting the rod 21 of the second cylinder device 19 into the feeder 14 of the molten metal 10 (see FIG. 4). ). The pressurizing speed in this case is the same as or faster than the pressurizing speed in the first stage.

In this case, according to the teachings of the conventional casting method, the feeder 14 is made to have a piston (product) by contraction when the molten metal 10 in the cavity 5 solidifies.
Is provided in order to prevent a cavity from being formed.
Therefore, the feeder 14 is provided facing a place where a cavity is likely to occur, that is, the cavity 5 forming the thick part of the piston (casting), and the feeder 14 is provided later than in the cavity 5 of the casting. Because it solidifies, this 14
The molten metal 10 in the cavity 5 is effectively pressurized by the piston rod, ie, the rod 21 and the guide cylinder 22 inserted therein.

In the casting step and the pressing step,
Part or all of the air in the cavity 5 is discharged from the pores of the upper mold 2 formed in a porous shape.

Therefore, the pressurizing step is performed at a pressure corresponding to the solidification of the molten metal 10, that is, when the molten metal 10 is mostly in a liquid phase, it is pressurized at a relatively low pressure, and
When 0 is pressurized with a high pressure, a part of the molten metal 10 is solidified particularly in the vicinity of the surface of the cavity 5 of the mold 1, so that the rigidity of the mold 10 and the casting machine needs to be particularly high. And a casting with excellent casting accuracy can be obtained.

Further, since the upper mold 2 is formed of a sintered metal material, air in the cavity 5 can be discharged from the pores of the upper mold 2 in the casting step and the pressurizing step.
It is possible to prevent a casting defect such as a blow hole from occurring, and to obtain a casting with high accuracy of shaping by the upper die 2, that is, high accuracy of the crown shape of the piston. In addition, since a coating die is not used for the upper mold 2, variation in shape accuracy due to variation in coating thickness can be advantageously avoided.

FIGS. 5 and 6 are drawings of an apparatus to which another embodiment of the present invention is applied. This embodiment is different from the above-described embodiment in that a step of pressurizing the molten metal is performed by using a riser of the molten metal. The point is that the air pressure is applied. In the description, the same components as those of the above-described embodiment are denoted by the same reference numerals, and the description thereof will not be repeated.

That is, in the apparatus for applying the present invention, the feeder 14 of the molten metal 10 is provided at two symmetrical positions,
A hollow air-introduction core 31 is provided on the upper part of the tube 4. The air introducing core 31 is attached to a ring core 32 provided on the outer periphery of the upper die 2 (see FIG. 6), and the upper end thereof is fixed to a flat adapter 33. Reference numeral 34 denotes a feeder core for providing the feeder 14.

A coupler 35 is screwed and fixed to the adapter 33 so as to face the hollow portion of the air introducing core 32. A pipe 36 is connected to the coupler 35, and the pipe 36 communicates with a compressor (not shown). In addition, the pipe 3
A valve 37 is provided in the middle of 6.

According to such a configuration, the casting process in which the molten metal 10 is filled in the cavity 5 of the mold 1 is the same as in the above-described embodiment, and is filled from a gate (not shown) under atmospheric pressure. You. Next, after the casting step, the valve 37 provided in the middle of the pipe 36 is opened by a predetermined amount to guide air from a compressor (not shown) into the hollow inside of the air introducing core 31, and the upper surface of the feeder 14 is added. The molten metal 10 is solidified by pressing (pressurizing step). Again,
In the same manner as in the above embodiment, the molten metal 10 is supplied at 2 to 5 kg / cm.
2 and a second step of applying a pressure of 10 to 25 kg / cm @ 2.

Therefore, in this embodiment,
In addition to providing the same functions and effects as described in the above embodiment, there is no mechanically sliding part such as a cylinder device when the molten metal 10 is pressurized, so that the casting is excellent in durability and easy to maintain. Machine.

Although the embodiment has been described with reference to the drawings, the specific configuration is not limited to this embodiment, and can be changed without departing from the spirit of the invention.

For example, in the embodiment shown in FIGS. 1 and 2, the first cylinder device 18 and the second cylinder device 1
Although the molten metal 10 is pressurized by using the cylinder 9, the rod of this cylinder device is connected to the feeder 1 by using one cylinder device.
4 may be moved forward and backward.

In the embodiment shown in FIGS. 5 and 6, the feeder 14 of the molten metal 10 is provided at two symmetrical positions, but the feeder 14 may be provided at one position.

Although the embodiment in which the molten metal 10 in the cavity 5 is pressurized in two stages has been described, the pressure may be continuously increased in accordance with the solidification of the molten metal.

[0041]

As described above in detail, according to the present invention, there is no need to particularly increase the rigidity of a mold and a casting machine, and a casting method capable of obtaining a casting with excellent casting accuracy. Is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an apparatus for applying an embodiment of the present invention to a method for casting a piston for an internal combustion engine.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a view showing a state where a first-stage pressurization is performed by a pressurizing device.

FIG. 4 is a view showing a state where a second-stage pressurization is performed by a pressurizing device.

FIG. 5 is a view similar to FIG. 2 showing another embodiment of the present invention.

FIG. 6 is a plan view of the ring core with the air introduction core attached.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Die 2 Upper mold 3 Lower mold 5 Cavity 10 Melt 14 Feeder 21 Rod (piston rod) 22 Guide cylinder (piston rod)

Claims (5)

[Claims] 1. A casting step of filling a cavity formed in a mold with a molten metal at atmospheric pressure, and after the casting step, pressurizing the cavity of the mold according to the degree of solidification of the molten metal. And a pressurizing step for solidifying the casting. 2. The step of pressurizing the molten metal, wherein when the molten metal near the cavity surface of the mold starts to solidify, 2-5 kg /
a first stage of pressurizing at a pressure of 10 cm2 / cm2 and a second stage of pressing at a pressure of 10 to 25 kg / cm2 when the molten metal in the cavity forming the thick part of the casting starts to solidify. The method for casting a casting according to claim 1, wherein the casting is characterized in that: 3. The method according to claim 1, wherein the step of pressurizing the molten metal is performed by a piston rod inserted into a riser of the molten metal. 4. The step of pressurizing the molten metal is performed by air pressure acting on a riser of the molten metal.
The method for casting a casting according to claim 1. 5. The method according to claim 1, wherein the mold having the cavity includes an upper mold and a lower mold having a gate, and the upper mold is formed of a sintered metal material. The method for casting a casting according to any one of claims 1 to 4.