JP2001012297A - Manufacture of piston for direct injection-type diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure the binding strength of a piston base material and a wear resisting ring and to improve a yield of the raw material by holding the wear resisting ring by a molding while separated from an inner wall surface of a die when the piston is casted with high pressure by setting the fiber molding for reinforcing a lip part and the wear resisting ring of the backing of a top ring groove in a die. SOLUTION: An annular recessed part 4a is formed on an upper outer peripheral side of a fiber molding 4a, an inner peripheral lower part of a wear resisting ring 5 is fitted to the recessed part 4a, and the wear resisting ring 5 is set in a die while separated from an inner wall surface 21 of an outer die 2. As the molten bath flows to a lower part of the outer die 2 through a clearance between the inner wall surface and the wear resisting ring 5 in high pressure casting, the thermal shrinkage of the wearing ring 5 by the outer die 2 can be prevented and the sufficient binding strength of a piston base material and the wear resisting ring 5 can be obtained. As the fiber molding 4 can be also used as a holding member of the wear resisting ring 5, an inner diameter of the outer die 2 can be reduced, and a cutting margin M for cutting the casting into the desired piston shape, can be reduced. Accordingly a yield of the raw material can be improved, and the cutting work can be simplified, which shortens a working time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a piston for a direct injection diesel engine having a combustion chamber formed at the head of the piston.

[0002]

2. Description of the Related Art Conventionally, as a method of manufacturing a piston of this type, a mold having a lower mold a, an outer mold b, and a core mold c as shown in FIG. The fiber molded body d for reinforcing the portion and the wear-resistant ring e serving as the base of the top ring groove of the piston are set, and in this state, an aluminum-based molten metal is injected into the mold and pressurized to perform high-pressure casting. There is known a method of cutting a casting into a predetermined piston shape shown by a virtual line in FIG.

[0003] If the wear ring e is in contact with the mold, the temperature of the wear ring e decreases due to heat shrinkage to the mold, and a sufficient bonding strength between the piston base material and the wear ring e is obtained. No longer available. Therefore, conventionally, a holding member f made of an annular fiber molded body that fits into the outer mold b is used, and a wear-resistant ring e is fitted into a concave notch portion on the inner peripheral side of the upper surface of the holding member f, and the wear-resistant ring e is fitted. e is set in the mold at a distance from the inner wall surface.

[0004]

In the above-mentioned prior art, the holding member f for the wear-resistant ring e is required and the cost is increased. Further, in order to prevent the displacement of the wear-resistant ring e during high-pressure casting, it is necessary to increase the outer diameter of the wear-resistant ring e to secure a certain amount of radial overlap of the wear-resistant ring e with respect to the holding member f. Therefore, the inner diameter of the outer mold b must be increased, and the stock removal in the cutting process of the cast product increases, and the material yield deteriorates.

[0005] In view of the above, the present invention provides a method of manufacturing a piston capable of securing the bonding strength between a piston base material and a wear-resistant ring without using a holding member and improving the material yield. The challenge is to do.

[0006]

Means for Solving the Problems In order to solve the above problems,
According to the present invention, there is provided a method for manufacturing a piston for a direct injection type diesel engine in which a combustion chamber is formed at the head of a piston, wherein the fiber molded body strengthens a lip portion of the combustion chamber and a base for a top ring groove of the piston. In a case where a piston is subjected to high pressure casting with a wear ring set in a mold, the molded body is held in a state where the wear ring is separated from an inner wall surface of the mold.

Also in the present invention, since the wear ring does not come into contact with the mold, it is possible to prevent the temperature of the wear ring from lowering due to heat shrinkage to the mold and to secure the bonding temperature between the piston base material and the wear ring. Further, according to the present invention, a dedicated holding member for holding the wear-resistant ring is not required, and the cost can be reduced. Furthermore, in order to secure the radial overlapping amount of the wear ring with respect to the holding member, it is not necessary to increase the outer diameter of the wear ring as in the related art, and it is possible to reduce the inner diameter of the mold and to reduce the material yield. Become good.

[0008]

FIG. 1 shows a casting mold for a piston for a direct injection type diesel engine. This mold
It has a lower mold 1 corresponding to the head side of the piston, an outer mold 2 corresponding to the outside of the body of the piston, and a core mold 3 corresponding to the inside of the piston, and is cast using a mold. The cast product was cut into the shape shown by the imaginary line in FIG.
And a piston P having three ring grooves Pb, Pc, and Pd on the outer periphery of the body.

In the mold, a fiber molded body 4 made of ceramic short fibers or whiskers for reinforcing the lip portion of the combustion chamber Pa and a base of the top ring groove Pb near the inner head of the three ring grooves are provided. A wear-resistant ring 5 made of niresist cast iron is set, and in this state, an aluminum-based molten metal is poured into a mold and pressed to perform high-pressure casting. A convex portion 11 corresponding to the combustion chamber Pa is formed at the center of the lower mold 1, and the fiber molded body 4 formed into an annular shape having a rectangular cross section is fitted on the outer periphery of the convex portion 11. Set in the mold.
An annular concave portion 4a is formed on the outer peripheral side of the upper surface of the fiber molded body 4.
The lower part of the inner circumference of the wear ring 5 is fitted into the recess 4a, and the wear ring 5 is set in the mold while being separated from the inner wall surface 21 of the outer mold 2. According to this,
During high-pressure casting, the molten metal smoothly flows toward the lower part of the outer mold 2 through the gap between the inner wall surface 21 and the wear-resistant ring 5, preventing the outer mold 2 from drawing off the heat of the wear-resistant ring 5, and the piston base material and the wear-resistant ring 5 is obtained.

Further, in this embodiment, since the fiber molded body 4 is also used as a holding member for the wear-resistant ring 5, a dedicated holding member f which has been conventionally used for setting the wear-resistant ring 5 becomes unnecessary. Needless to say, it is not necessary to increase the outer diameter of the wear ring 5 in order to secure a radial overlapping amount of the wear ring 5 with the holding member f, and the inner diameter of the outer mold 2 can be reduced. Therefore, the cutting allowance M for cutting the cast product into a required piston shape is reduced. That is,
In the conventional method using the holding member f, the cutting allowance m is about 4 mm, whereas the cutting allowance M in the method of the present embodiment is about 4 mm.
Is about 1 mm. Since the cutting allowance is reduced as described above, the material yield is improved, and the cutting process is simplified and the processing time can be reduced.

[0011]

As is apparent from the above description, according to the present invention, the joint strength between the piston base material and the wear-resistant ring can be ensured without using a dedicated holding member for holding the wear-resistant ring.
The machining allowance after casting can be reduced to improve the material yield, and the manufacturing cost of the piston can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a main part of a mold showing a set state of a molded body and a wear ring according to the method of the present invention

FIG. 2 is a sectional view of a conventional example corresponding to FIG.

[Explanation of symbols]

 21 inner wall surface 4 fiber molded body 5 wear ring P piston Pa combustion chamber Pb top ring groove

Claims (1)

[Claims] 1. A method of manufacturing a piston for a direct injection type diesel engine, wherein a combustion chamber is formed at the head of the piston,
A high-pressure casting of a piston in a state in which a fiber molded body for reinforcing a lip portion of a combustion chamber and a wear ring serving as a base for a top ring groove of the piston are set in a mold, wherein the wear ring is formed of the mold. A method for manufacturing a piston for a direct injection diesel engine, wherein the piston is held on the molded body while being separated from an inner wall surface.