JPH06330106A - Method for hot-forming piston from aluminum alloy powder - Google Patents

Abstract

PURPOSE:To provide a method for hot-forming a piston from an aluminum alloy powder, with which insufficient strength of the upper part of the pin boss part due to the defective joining integration can be prevented from occurring. CONSTITUTION:The method for hot-forming a piston from an aluminum alloy powder is performed by inserting a green compact of the Al alloy powder into the molds 2, 4 and 5 for forming the piston, pressing the forming mold 4, which has the forming surface 6 for forming the inner surface of the piston including the pin boss part, on the green compact and allowing the green compact to plastic-flow to hot-form the Al alloy powder into a prescribed shape. The forming surface 6 of the forming mold 4 is provided with the recessed part 7 for accelerating the plastic flow of the part of the green compact which is used for forming the upper part 12A of the pin boss part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for hot forming an Al (aluminum) alloy powder to produce a piston.

[0002]

2. Description of the Related Art Parts used in internal combustion engines such as automobiles and motorcycles, such as pistons, connecting rods, brake rotors, and the like, must have strength to withstand vigorous motion at high temperatures. On the other hand, in recent years, weight reduction of parts has been desired from the viewpoint of weight reduction of automobiles and energy saving. Therefore, the parts requiring high-temperature strength are also being formed of Al alloys (JIS 2000 series high-strength Al alloys).

However, the molten Al alloy has a limit in the content of alloying elements, which in turn limits the high temperature strength. Therefore, in order to improve the high-temperature strength, it is possible to subject the green compact of the rapidly solidified powder of Al alloy containing Si or Fe to supersaturation to hot plastic working to generate plastic flow and form it into a predetermined shape. Being tried. The molded product hot-formed by such rapidly solidified Al alloy powder has excellent material properties that the ingot alloy material does not have. An oxide film is formed on the surface of the Al alloy powder, but this oxide film is divided in the process of plastic flow, and the powders are joined and integrated.

[0004]

When a piston is hot-formed by using an Al alloy powder, a compact of the Al alloy powder is charged into a molding die, and the piston including the pin boss portion is included in the compact. A molding die having a molding surface for molding the inner surface is pressed to plastically flow the green compact and hot-molded into a predetermined shape. At this time, since the plastic flow of the green compact is less likely to occur in the upper part of the pin boss portion and the amount of plastic deformation is small, an oxide film remains on the powder surface and the bonding and integration of the powders are insufficient, resulting in insufficient strength. There's a problem.

The present invention has been made in view of the above problems, and provides a hot forming method for a piston for an internal combustion engine capable of preventing the occurrence of insufficient strength at the upper portion of the pin boss due to defective joint integration of Al alloy powder. The purpose is to provide.

[0006]

The hot forming method of the present invention comprises:
A powder compact of Al alloy powder is loaded into a piston molding die, and the powder compact is pressed against a molding die having a molding surface for molding the inner surface of a piston including a pin boss portion. In a hot forming method of a piston using an Al alloy powder which is plastically flowed to be hot formed into a predetermined shape, a recess is provided on the forming surface for promoting plastic flow of the pin boss upper forming powder of the green compact. There is.

[0007]

Since the concave surface is provided on the molding surface of the molding die for promoting the plastic flow of the powder for molding the pin boss upper portion of the powder compact, the molding die is pressed against the powder compact of the Al alloy powder and hot pressed. When molding, if the concave portion is not present, the molding powder on the upper portion of the pin boss, which is less likely to cause plastic flow of the green compact, is plastically deformed and plastically flows into the concave portion. The alloy powders are joined and integrated.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a hot-molded state of a piston. A die for piston molding is a substrate 1 and a die holder 3
And a lower mold 5 slidably inserted into the molding holes of the mold main body 2, and a pin boss portion is formed on the lower surface of the upper mold 4. A molding surface 6 is formed for molding the inner surface of the piston including the piston. still,
A heater (not shown) is attached to the outer periphery of the mold body 2.

To hot-mold a piston, a compact of Al alloy powder preheated to around the hot-molding temperature is charged into the molding hole of the mold body 2 in which the lower mold 5 is inserted, The upper die 4 inserted into the upper opening of the die body 2 is slid to the lower die side to hot press the green compact. In the molding process, the green compact is divided and integrated by plastic flow due to plastic flow, and is molded into a piston 11 having a predetermined shape as shown in FIG. After molding, the lower die 5 is pushed up and the molded product is taken out.

In the conventional hot forming, the piston 11
Since plastic flow is unlikely to occur in the upper portion 12A of the pin boss portion 12, the oxide film on the powder surface remains, the bonding and integration of the powder particles are not complete, and the strength of the pin boss portion 12 is insufficient. In this embodiment, as shown in FIGS. 2 and 3, a recess 7 for plastically flowing the pin boss upper molding powder of the green compact is formed in the pin boss upper molding portion of the molding surface 6 of the upper mold 4. The portion 8 is recessed along the axial direction.

By hot forming using the upper mold 4 in which the concave portion 7 is formed, the molding powder on the upper portion of the pin boss, which is less likely to cause plastic flow, will plastically flow into the concave portion 7 and the pin boss portion. In the upper part 12, Al alloy powders including the upper part 12A are joined and integrated to increase the strength. The convex portion formed by the concave portion 7 may be cut off at the time of machining after molding, or may remain. Further, as the Al alloy powder for piston forming, Al-20% Si alloy, Al-1 having excellent high temperature strength and wear resistance is used.
A rapidly solidified powder of heat resistant Al alloy such as 5Fe alloy is used.

[0012]

According to the hot forming method of the present invention, since the concave surface for promoting the plastic flow of the powder for molding the pin boss upper portion of the green compact is provided on the molding surface of the molding die,
l When pressing into a powder compact of an alloy powder and performing hot forming, if the recess is not present, the molding powder on the upper portion of the pin boss where the plastic flow of the powder compact is less likely to be plastically flowed into the recess. The Al alloy powders in the upper portion of the pin boss portion are joined and integrated, and high strength is secured in the pin boss portion.

[Brief description of drawings]

FIG. 1 is an overall cross-sectional view showing a molding state of a piston molding die according to an embodiment.

FIG. 2 is an enlarged sectional view of an essential part showing a molding state of a piston molding die according to an embodiment.

FIG. 3 is an enlarged cross-sectional view of an essential part showing a molding state of a piston molding die when a recess for plastic flow promotion is viewed from the front.

[Explanation of symbols]

 2 Mold main body 4 Upper die (molding die) 5 Lower die 6 Molding surface 7 Recessed portion 12 Pin boss portion 12A Pin boss upper portion

Claims (1)

[Claims] 1. A compact for Al alloy powder is loaded into a piston molding die, and a compact having a molding surface for molding the inner surface of a piston including a pin boss portion is pressed against the compact.
In a hot forming method for a piston using an Al alloy powder, which plastically flows the green compact into a predetermined shape by hot forming, a plastic flow of the pin boss upper forming powder of the green compact is promoted on the forming surface. A hot forming method for an Al alloy powder, characterized in that a recess is provided.