JP2001071119A - Preform and method for inserting preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the tensile stress caused by high cycle fatigue by disposing a shrinkage restraining member which is abutted on an insered core and restrains the thermal shrinkage of the core, and pouring molten metal. SOLUTION: The shrinkage restraining member 42 for restraining the thermal- shrinkage of the salt core 26 is joined with a preform 41 for lip part, and after separately heating up the salt core 26 and the preform 41 for lip part, the salt core 26 is fitted to the shrinkage restraining member 42 to be held to pour molten metal. The salt core 26 having thermal-expansion coefficient larger than that of the preform 41 for lip part is inserted in the state of adding the residual stress. The preform 41 is inserted into the lip part in a combustion chamber formed at the tip part of a piston in an engine for car, and it is desirable to insert the other preform 41 into the groove part of a piston ring. The preheating temperature is 300-600 deg.C and the temperature when it is disposed into a mold, is desirable to be (the preheating temperature -50 deg.C) to (the preheating temperature -300 deg.C).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a preformed body to be cast in order to strengthen a piston lip portion or a piston ring groove of a combustion chamber formed in, for example, an engine piston of an automobile, and a method of casting the preformed body. About.

[0002]

2. Description of the Related Art Aluminum alloys are widely used in automobile engine parts because of their light weight and good thermal conductivity.

When an automotive piston is cast from an aluminum alloy, a porous preform may be impregnated with a molten metal and then cast to reinforce the piston lip portion, the piston ring groove, and the like.

[0004] As a technique for casting the preformed body, Japanese Patent Application Laid-Open No. 9-253827 discloses that a core having a larger coefficient of thermal expansion than the preformed body is used, and the core is expanded by preheating to form the preformed body. There is disclosed a method of holding the inner circumference.

[0005]

By the way, taking a piston for a diesel engine as an example, as shown in FIG. 14, the higher the output of the diesel engine, the more the combustion formed on the top surface of the piston for the diesel engine. In the chamber, the explosive force G acts as a high cycle fatigue to expand the combustion chamber, whereby the tensile stress F1 repeatedly acts in a direction orthogonal to the piston pin. Therefore, it is necessary to reduce the tensile stress F1 acting on the top surface forming the combustion chamber.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a preform that can be cast in a state where a compressive residual stress is applied to the preform and reduce tensile stress due to high cycle fatigue, and a method of casting the preform. .

[0007]

In order to solve the above-mentioned problems and achieve the object, the preformed body of the present invention has a core having a higher coefficient of thermal expansion than that of the preformed body, which is locked after preheating, and melts the molten metal. In a preform which is poured into a mold, impregnated with a molten metal, and cast, a shrinkage suppressing member which abuts on the core and suppresses thermal shrinkage of the core is provided.

[0008] Preferably, the preform and the core are preheated separately.

Further, the method of casting and casting a preform of the present invention preheats a preform and a core having a higher coefficient of thermal expansion than the preform so that the heat shrinkage of the core can be suppressed. Then, the core is locked to the preformed body, the preformed body in which the core is locked is arranged in a mold, and a molten metal is poured into the mold to impregnate the molten metal into the preformed body. Cast in.

Preferably, the core is locked to a shrinkage suppressing member provided on the preform.

Preferably, the preform is cast in a lip portion of a combustion chamber formed on the top of a piston of an automobile engine, and another preform is cast in a piston ring groove.

Preferably, each of the preforms is preheated separately.

[0013]

As described above, according to the first aspect of the present invention, the shrinkage suppressing member for suppressing the heat shrinkage of the core by contacting the core having a higher coefficient of thermal expansion than the preformed body is provided. As a result, the preform can be cast in a state where a compressive residual stress is applied, and the tensile stress due to high cycle fatigue can be reduced. Further, the core can be easily held.

According to the second aspect of the present invention, since the preformed body and the core are preheated separately, it is possible to easily apply a compressive residual stress to the preformed body by the cores having different heat shrinkage amounts.

According to the third aspect of the present invention, the preform is
A core having a larger coefficient of thermal expansion than the preformed body is preheated, and the core is locked to the preformed body in a state where thermal contraction of the core can be suppressed. The molded body is placed in a mold, the molten metal is poured into the mold, and the preformed body is impregnated with the molten metal and cast. Tensile stress can be reduced. Further, the core can be easily held.

According to the fourth aspect of the present invention, the core is engaged with the shrinkage suppressing member provided on the preformed body, so that the core is cast in a state where a compressive residual stress is applied to the preformed body. Tensile stress due to high cycle fatigue can be reduced. Further, the core can be easily held.

According to the invention of claim 5, the preform is
By being cast in the lip of the combustion chamber formed on the top of the piston of the automobile engine and another preform in the piston ring groove, compressive residual stress is applied to the lip, The piston ring groove can be strengthened.

According to the invention of claim 6, each preform is preheated separately, so that the preform and the core are preheated separately, so that each preform is adapted to each preform. Preheating can be performed under optimal preheating conditions.

[0019]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. [Cast-In Member] FIG. 1 is a partial cross-sectional view of a piston for a diesel engine in which the preform of the present embodiment is cast-in.

As shown in FIG. 1, an aluminum alloy piston 1 (hereinafter abbreviated as piston 1) exemplified as a cast-in member of the present embodiment is manufactured by a gas pressure casting apparatus described later, A top ring groove 3 for fitting a top ring, a secondary ring groove 4 for fitting a secondary ring, and an oil ring groove 5 for fitting an oil ring are formed in the outer peripheral portion. Further, a cooling oil passage 7 is formed near the top ring groove 3 and radially inside the piston main body 2. The piston 1 is for a direct injection diesel engine,
A combustion chamber 30 in which a groove of a predetermined shape is formed annularly and uniformly is formed on the top surface of the piston. Further, the combustion chamber 30 is formed with an annular lip portion 31 whose opening edge slightly protrudes in the axial direction and defines an entrance to the combustion chamber 30. The piston 1 is formed with a piston pin insertion hole 8 that penetrates the piston body 2 along the diametric direction.

The top ring groove 3 of the piston 1 is integrally cast with the annular ring groove preform 40 as a cast-in portion 6 as described later, and the lip portion 31 of the piston 1 is also formed as described later. The piston body 2 other than the top ring groove 3 and the lip part 31 is cast with an aluminum alloy as a cast-in part 32 integrally with the annular lip part preform 41.

The cast-in portion 6 of the top ring groove 3 is formed, for example, by arranging a pre-formed body composed of porous ceramic particles / fibrous formed body in a mold, impregnating with an aluminum alloy melt, and solidifying. Is done.

The cast-in portion 32 of the lip portion 31 is formed by placing a preform containing a metal fiber material made of stainless steel or the like in a mold, impregnating with an aluminum alloy melt, and solidifying.

Incidentally, the cast-in portion 6 of the top ring groove 3 may be compounded with a preform containing a metal fiber material.

As the metal fiber material, besides stainless steel, there are tungsten, molybdenum, carbon steel and the like, but stainless steel fiber material is practical since it has the highest strength and is inexpensive. [Gas Pressure Casting Apparatus] The piston 1 is shown in FIGS.
It is manufactured by the gas pressure casting apparatus shown in FIG. 2 and 3 are schematic cross-sectional views of the gas pressure casting apparatus of the present embodiment in directions orthogonal to each other.

As shown in FIGS. 2 and 3, a gas pressure casting apparatus 10 of the present embodiment includes outer molds 12L and 12R which are split molds which are divided into right and left molds 11 and a middle mold arranged below. 13 and an upper die 14 having a feeder portion 14a disposed above, and a product part cavity 15 is formed therein. In the mold 11, a ring groove preform 40 is disposed at a location corresponding to the top ring groove 3, and a lip preform 41 is disposed at a location corresponding to the lip 31. The hot water portion 14a has a pipe 16 for applying air pressure from the hot water portion 14a.
Is attached. Reference numeral 17 denotes a cast pin for forming a piston pin insertion hole.

The outer dies 12L and 12R can be driven by outer cylinders 18L and 18R, the middle die 13 can be driven by a middle cylinder 19, and the upper die 14 can be driven by an upper cylinder 20.

In the middle of the pipe 16, there is provided a valve 27 for selectively communicating the feeder section 14a with a pressurized air source and the atmosphere. A cover 2 provided with a cooling mechanism such as a water-cooled copper lump 28
3, the gate 22 is closed, and at the same time, the valve 16 is operated to connect the pipe 16 to the pressurized air source.
From 6, the factory air may be injected to pressurize the molten metal. With this configuration, there is an advantage that the vicinity of the cast-in portion can be effectively pressurized.

Reference numeral 25 designates a runner leading from the gate 22 to the product cavity 15, and reference numeral 26 designates a spare lip portion for suppressing heat shrinkage by suppressing means to be described later for forming a cooling oil passage in the piston. The salt core held by the molded body 41.

In the above configuration, after pouring a molten metal of an aluminum alloy (for example, JIS standard AC8A) from the sprue 22, the cover 23 is lowered to seal the sprue 22, and at the same time, the pipes 16 to 10 provided in the cover 23 are provided. Factory air having a pressure of less than atmospheric pressure (for example, 0.5 to 10 kg / cm2) is injected to pressurize the molten metal for about 50 seconds to 1 minute. At the time of pressurization by air, a part of the molten metal flows into the air vent groove 21 and is cooled and solidified in the air vent groove 21 to seal the air vent groove 21. Then, the molten metal solidified in the air vent groove 21 is removed as burrs as the mold 11 is divided. In addition, pressurization by the above air is 10 to 10 minutes after pouring.
It must start within 30 seconds, but this time range
Generally, the time may be set to a time range in which pressure can be effectively applied before solidification of the molten metal. [Arrangement in Mold] FIG. 4 is a sectional view showing the arrangement of the ring groove preform, the lip part preform, and the salt core in the mold. FIG. 5 is a diagram illustrating a state in which a compressive residual stress is applied by the shrinkage suppressing member. FIG. 6 is a diagram showing the amount of heat shrinkage between the lip portion preform and the salt core.

As shown in FIG. 4, the salt core 26 is held by the lip portion preform 41, and the ring groove preform 4 is formed.
0 is disposed separately from the upper ends of the outer dies 12L and 12R.

The difference between the heat shrinkage of the salt core 26 and the preformed body 41 for the lip between the salt core 26 and the preformed body 41 for the lip portion after the preheating of the salt core 26 and the preformed body 41 for the lip part is obtained. A compressive residual stress is applied to the lip preform 41. For this reason, as shown in FIG. 4, the temperature of the salt core 26 and the lip portion preform 41 is separately raised, and after the temperature is raised to the preheating temperature, the salt core 26 and the lip portion preform 41 are formed. With a heat-resistant adhesive. Also, as shown in FIG.
After the shrinkage suppressing member 42 for suppressing the thermal shrinkage of the salt core 26 is joined to the lip portion preform 41, and the salt core 26 and the lip portion preform 41 are separately heated, The shrinkage suppressing member 42 of the preformed body 41 for the lip portion is
To be held.

The salt core 26 and the lip preform 41 are taken out of the preheating furnace and are naturally cooled while being placed in the mold. As shown in FIG. 6, the thermal expansion coefficient (for example, in the case of stainless steel fiber) of the lip portion preform 41 is
17 × 10 ⁻⁶ / ° C., thermal expansion coefficient of salt core 26 is 45 × 1
At 0 ⁻⁶ / ° C., the thermal expansion coefficient of the salt core is larger than that of the lip preform 41.

Thus, the lip portion preform 41 is cast in a state where the compressive residual stress due to the heat shrinkage of the salt core 26 is added during natural cooling, thereby reducing the tensile stress applied to the lip portion due to high cycle fatigue. it can. In addition, preheating can be performed under optimum preheating conditions according to each preform.

The preheating temperature is desirably 300 to 600 ° C.
If the temperature is lower than 300 ° C., the cast-in property deteriorates. The temperature at the time of disposing in the mold is preferably a preheating temperature minus 50 ° C to a preheating temperature minus 300 ° C. If the difference from the preheating temperature is less than 50 ° C., sufficient compressive residual stress cannot be applied, and if it is 300 ° C. or more, cast-in property deteriorates. [Application of Adhesive to Salt Core] FIG. 7 is a view for explaining a method of applying an adhesive to the salt core.

As shown in FIG. 7, when the salt core is bonded to the lip portion preform, an adhesive is applied to the entire surface of the salt core, so that fine cracks remain in the salt core. However, it is possible to prevent the burr 7a from being generated due to the insertion of the molten metal. FIG. 8 is a view showing a cast-in shape 1 of the lip portion preform. FIG. 9 is a sectional view taken along line II of FIG. FIG. 10 is a view showing a cast-in shape 2 of the lip portion preform.

As shown in FIGS. 8 and 9, the lip preform 41 is disposed at least in a direction perpendicular to the direction of the piston pin, and the outer edges thereof are the upper die 14 and the outer die 12L,
It is cast in the lip part on the piston pin side in a state of contacting the mold splitting surface of 12R. With this arrangement, the tensile stress F1 acting in a direction perpendicular to the piston pin can be reduced so that the explosive force expands the combustion chamber as high cycle fatigue.

Further, cooling can be suppressed by arranging the ring groove preform 40 and the lip portion preform 41 so as to overlap each other in the cavity.

Also, since the outer edge of the lip portion preform 41 is in contact with the parting surface 14b, gas can be released from the parting surface instead of the air vent groove 21.

As shown in FIG. 10, the lip preform 41 may be arranged along the opening edge of the lip in a direction perpendicular to the piston pin direction. Example 1 FIG. 11A is a view showing a holding state of a salt core and a preform for a lip portion as Example 1, and FIG.
It is the figure seen from the direction.

In Example 1, a stainless steel fiber compact was used as the lip preform and a TiO2 particle compact was used as the ring groove preform. As shown in FIG. 11, the stainless fiber molded body is annular and has a groove 41 for positioning the salt core.
a was formed over the entire circumference, and the stainless steel fiber molded body and the salt core were not joined to each other, but were placed in a preheating furnace and maintained at 400 ° C.
While maintaining the temperature at 400 ° C., three places 2 on the upper end face of the salt core
An MgO-SiO2 powder paste was applied to 6a to 26c, and a stainless fiber molded body was adhered. 600 ° C in another preheating furnace
After placing the preheated TiO2 particle compact in the mold, remove the stainless fiber compact and the salt core from the preheating furnace and remove
After cooling to 00 ° C., it was placed in a mold, and the aluminum alloy AC8A was filled in the mold to cast a piston for a diesel engine.

In the first embodiment, the salt core can be disposed in the mold with good productivity and the productivity can be reduced without damaging the TiO2 particle molded body, and the tensile stress generated in the lip can be reduced. Was. Similar results were obtained when a carbon steel fiber molded body was used as the lip portion preform and an alumina short fiber molded body was used as the ring groove preform. [Example 2] In Example 2, a stainless fiber molded body was used as the lip preform and a TiO2 particle molded body was used as the ring groove preform. As shown in FIG. 11, the stainless fiber molded body is annular and has a groove 41 for positioning the salt core.
a was formed over the entire circumference, and the stainless steel fiber molded body and the salt core were not joined to each other, but were placed in a preheating furnace and maintained at 400 ° C.
With the temperature maintained at 400 ° C., an MgO—SiO 2 powder paste was applied to the entire surface of the salt core, and the stainless fiber molded body was adhered. After placing the TiO2 particle compact preheated to 600 ° C in another preheating furnace in the mold, the stainless steel fiber compact and the salt core were taken out of the preheating furnace, cooled to 300 ° C, and then placed in the mold, A piston for a diesel engine was cast by filling the mold with alloy AC8A.

In the second embodiment, the salt core can be arranged in the mold with good productivity and the productivity can be reduced without damaging the TiO2 particle molded body, and the tensile stress generated in the lip can be reduced. Was. In addition, generation of burrs in the cooling oil passage could be suppressed. Example 3 FIG. 12 (a) is a view showing a holding state of a salt core and a preform for a lip portion as Example 3, and FIG.
It is the figure seen from the direction.

In Example 3, a stainless steel fiber molded article was used as the lip preform and a TiO2 particle molded article was used as the ring groove preform. As shown in FIG. 12, the stainless fiber molded body is provided in an annular shape and provided with a shrinkage suppressing member 42 for suppressing thermal shrinkage of the salt core, and the stainless steel fiber molded body and the salt core are connected to a preheating furnace without being joined. And kept at 400 ° C. 40
While maintaining the temperature at 0 ° C., the three shrinkage suppressing members 42 a to 4
2c was inserted into three places on the inner peripheral surface of the salt core, and the salt core was fitted and held. After placing the TiO2 particle compact preheated to 600 ° C in another preheating furnace in the mold, the stainless steel fiber compact and the salt core were taken out of the preheating furnace, cooled to 300 ° C, and then placed in the mold, A piston for a diesel engine was cast by filling the mold with alloy AC8A.

According to the first and second embodiments, the salt core can be arranged in the mold with good productivity and the productivity can be reduced without damaging the TiO2 particle molded body, and the tensile stress generated in the lip portion can be reduced. I was able to. Similar results were obtained when a carbon steel fiber molded body was used as the lip portion preform and an alumina short fiber molded body was used as the ring groove preform. Example 4 FIG. 13A is a view showing a holding state of a salt core and a preform for a lip portion as Example 4, and FIG.
It is the figure seen from the direction.

In Example 4, a stainless fiber compact was used as the lip preform and a TiO2 particle compact was used as the ring groove preform. As shown in FIG. 13, the stainless steel fiber molded article is provided in a strip shape and provided with a shrinkage suppressing member 42 for suppressing the thermal shrinkage of the salt core, and the stainless steel fiber molded article and the salt core are not joined to the preheating furnace without joining. And kept at 400 ° C. 40
While maintaining the temperature at 0 ° C., the three shrinkage suppressing members 42 a to 4
2c was inserted into three places on the inner peripheral surface of the salt core, and the salt core was fitted and held. After placing the TiO2 particle compact preheated to 600 ° C in another preheating furnace in the mold, the stainless steel fiber compact and the salt core were taken out of the preheating furnace, cooled to 300 ° C, and then placed in the mold, A piston for a diesel engine was cast by filling the mold with alloy AC8A.

In the fourth embodiment, the salt core can be disposed in the mold with good productivity and the production cost can be reduced without breaking the TiO2 particle molded body, and the tensile stress generated in the lip can be reduced. Was. Similar results were obtained when a carbon steel fiber molded body was used as the lip portion preform and an alumina short fiber molded body was used as the ring groove preform.

The above is a description of the embodiments and examples of the present invention. The aluminum alloy member manufactured according to the present invention is applied to a piston for a diesel engine by the gas pressure casting method as in the above-described embodiment. The present invention is not limited to this, and can of course be applied to the production of bearing caps, connecting rods, and cylinder heads by other casting processes. Further, according to the present invention, other light alloy castings such as a magnesium alloy can be manufactured in addition to the aluminum alloy.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of a piston for a diesel engine in which a preform of the present embodiment is cast-in.

FIG. 2 is a schematic cross-sectional view of a gas pressure casting apparatus of the present embodiment in a direction orthogonal to each other.

FIG. 3 is a schematic cross-sectional view of a gas pressure casting apparatus of the present embodiment in a direction orthogonal to each other.

FIG. 4 is a sectional view showing the arrangement of a ring groove preform, a lip portion preform, and a salt core in a mold.

FIG. 5 is a diagram illustrating a state in which a compressive residual stress is applied by a shrinkage suppressing member.

FIG. 6 is a view showing the amount of heat shrinkage between a preform for a lip portion and a salt core.

FIG. 7 is a diagram illustrating a method of applying an adhesive to a salt core.

FIG. 8 is a view showing a cast-in shape 1 of the lip portion preform.

FIG. 9 is a sectional view taken along the line II of FIG. 8;

FIG. 10 is a view showing a cast-in shape 2 of the lip portion preform.

11A is a diagram showing a holding state of a salt core and a preform for a lip portion as Example 1, and FIG. 11B is a diagram viewed from a direction A.

12A is a view showing a holding state of a salt core and a preform for a lip portion as Example 3, and FIG. 12B is a view seen from a direction B. FIG.

13A is a diagram showing a holding state of a salt core and a preform for a lip portion as Example 4, and FIG. 13B is a diagram viewed from a direction C. FIG.

FIG. 14 is a diagram illustrating a tensile stress applied to a piston lip due to an explosive force.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Aluminum alloy piston 2 ... Piston main body 3 ... Top ring groove 6 ... Cast-in part 11 ... Mold 12L, 12R ... Outer mold 12b, 14a ... Feeder part 14 ... Upper mold 15 ... Product part cavity 16 ... Pipe 21, 24 ... air vent groove 22 ... gate 23 ... cover 26 ... salt core 40 ... preformed body for ring groove 41 ... preformed body for lip part 42 ... shrinkage suppressing member

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F02F 5/00 F02F 5/00 N

Claims (6)

[Claims] 1. A preformed body having a larger coefficient of thermal expansion than a preformed body is locked after preheating, and a molten metal is poured into a mold to be impregnated with the molten metal and cast. A preform having a shrinkage suppressing member for suppressing heat shrinkage of the core. 2. The preform according to claim 1, wherein the preform and the core are preheated separately. 3. A preformed body and a core having a higher thermal expansion coefficient than the preformed body are preheated, and the core is engaged with the preformed body in a state where thermal contraction of the core can be suppressed. A method of casting in which the preform having the core locked thereon is placed in a mold, and a molten metal is poured into the mold to impregnate the preform with the molten metal and cast. 4. The core according to claim 3, wherein the core is locked to a shrinkage suppressing member provided on the preform.
3. The method of casting in according to 1. 5. The preform is cast in a lip of a combustion chamber formed on a top of a piston of an automobile engine, and another preform is cast in a piston ring groove. The cast-in method according to claim 3 or 4. 6. The method according to claim 5, wherein each of the preforms is preheated separately.