JPH0813003A - Method for hot-compacting metal powder - Google Patents

Abstract

PURPOSE:To provide a method for hot-compacting metal powder by which seizing is hardly caused on the compacting face of a metal mold even at a part at which high plastic fluidization is carried out. CONSTITUTION:Compacting stock 10 is put in a metal mold for compacting, a compacting die for forming the outside or inside of a compact is pressed on the stock 10 and the stock 10 is brought into plastic fluidization and hot- compacted into a specific shape. The stock 10 is obtd. by coating the periphery of a green compact 11 of metal powder with a metallic film 12 for lubrication excellent in ductility. The metallic film 12 is preferably formed by plating or thermal spraying.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot forming method for metal powder such as Al alloy powder, which is unlikely to cause seizure.

[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. For this reason, Al alloys (JIS 2000 series high-strength Al alloys) are also used for parts requiring high-temperature strength.
May be formed by.

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, a rapidly solidified powder of an Al alloy containing Si or Fe in a supersaturated state is used, and this green compact is subjected to hot plastic working to generate a plastic flow to obtain a predetermined shape. Attempts have been made to shape. The molded product hot-molded by such rapidly solidified 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]

However, during hot forming, a portion having a large plastic flow occurs in the green compact of the Al alloy powder depending on the shape of the molded product. That is, the molding die is pushed into the green compact of the Al alloy powder charged in the die,
When molding is performed between the inner surface of the mold and the outer surface of the molding die, there is a portion where the plastic flow violently flows along the inner surface of the die and the outer surface of the molding die.

Usually, in order to prevent seizure between the material and the mold, a lubricant such as oily graphite is applied to the molding surface of the mold. However, since the Al alloy powder contains a relatively large amount of alloy components, it is a material that is difficult to plastically flow,
Since the frictional force becomes large in the portion where the plastic flow is large, the lubricant is interrupted and seizure easily occurs. Once the seizure occurs, it takes time for the maintenance of the mold and the productivity is remarkably reduced. Such a problem occurs not only in hot forming of Al alloy powder but also in Ti alloy powder, for example.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a hot forming method for a metal powder in which seizure hardly occurs on a forming surface of a mold or the like even in a portion having a large plastic flow.

[0007]

The hot forming method of the present invention comprises:
The molding material is charged into a molding die, and a molding die for molding the outer surface or the inner surface of the molded product is pressed against the molding material,
In the molding method in which the molding material is plastically flowed to be hot-molded into a predetermined shape, the molding material is obtained by coating the outer peripheral surface of a metal powder compact with a lubricating metal film having excellent ductility.
The lubricating metal film may be formed by plating or thermal spraying.

[0008]

[Function] Since the outer peripheral surface of the powder compact of the metal powder is coated with the lubricating metal film having excellent ductility, the powder compact does not come into direct contact with the molding surface of the mold or the like during hot forming. The metal film for lubrication formed on the surface of the material easily plastically flows along the molding surface of the mold or the like and has a small frictional force with the molding surface, so that seizure is prevented. The lubricating metal film can be easily formed on the outer peripheral surface of the green compact by plating or thermal spraying.

[0009]

EXAMPLE A hot forming of an Al alloy piston for an internal combustion engine will be described as an example. FIG. 1 shows a molding material 10 according to the present invention.
The metal film 12 for lubrication is formed on the outer peripheral surface of the green compact 11 of Al alloy powder by a metal having excellent ductility. As the Al alloy powder, Al-20 wt% S
A rapidly solidified powder of a heat-resistant and high-strength Al alloy such as an i alloy and an Al-10 wt% Fe alloy is suitable. On the other hand, the metal film 12 does not melt at the hot forging temperature and has excellent ductility, such as pure A.
1, pure Zn, and the main components (preferably Al or Zn)
Al alloys and Zn alloys having a content of 95 wt% or more). As a means for forming the metal film 12,
The metal film 12 can be easily and uniformly formed on the outer peripheral surface of the green compact 11 by immersion plating or thermal spraying, resulting in excellent productivity.
Immersion plating can process a large amount of materials at once,
Especially excellent in productivity. The film thickness of the metal film 12 should be such that a continuous film can be maintained at the time of molding, and a film thickness of about 100 μm or more is sufficient.

FIG. 2 shows a hot-molding state of the piston. A molding die is fixed to a substrate 1 by a die holder 3 and slides on a die body 2 and a die hole of the die body 2. It is composed of an upper die 4 and a lower die 5 which are freely inserted and attached.
The inner surface of the molding hole is a molding surface of the outer peripheral surface of the piston,
The lower surface of the upper mold 4 is a molding surface 6 for molding the inner surface of the piston. A heater (not shown) is attached to the outer periphery of the mold body 2.

To hot-mold a piston, a lubricant such as oily graphite is applied to the molding hole of the mold body 2 in which the molding surface 6 of the upper mold 4 and the lower mold 5 are inserted, and then the molding hole is formed. Into the molding material 10 preheated to around the hot molding temperature, the upper mold 4 inserted into the upper opening of the mold body 2 is slid to the lower mold side and pushed into the molding material 10. Hot press molding. During the molding process, the green compact is separated by plastic flow due to plastic flow and is integrated, and the piston 1 having a predetermined shape is formed.
4 is molded. After molding, the lower die 5 is pushed up and the molded product is taken out.

When hot forming is performed using the forming material 10 covered with the lubricating metal film 12, the skirt portion 15 of the piston 14 is formed by a large plastic flow. At this time, the outer peripheral surface of the skirt portion 14 and Since the lubricating metal film 12 extends on the surface of the inner peripheral surface to form a coating layer,
Since the Al alloy inside the skirt portion 15 does not come into direct contact with the molding surface, seizure does not occur in the skirt portion 15. Also, although the skirt portion 15 is thin, the deformation resistance is small, and the moldability is also improved. To do. After forming, when the piston is finished, the stretched coating layer of the lubricating metal film adhered to the outer peripheral surface of the piston is removed, but the coating layer on the inner surface has no problem in performance, so leave it as it is. You may stay.

The present invention can be applied not only to the hot forming of the piston but also to the hot forming of various lightweight metal molded products such as Al alloy and Ti alloy.

[0014]

According to the hot forming method of the present invention, since the forming material has the metal film for lubrication excellent in ductility formed on the outer peripheral surface of the green compact of the metal powder, the metal mold or the forming die is formed at the time of forming. It is possible to smoothly stretch the metal film along the molding surface, reduce frictional force with the molding surface, prevent seizure with the molding surface, improve moldability, and improve productivity. . Further, by applying plating or thermal spraying as a means for coating the lubricating metal film, the formation of the metal film becomes extremely easy and the productivity is excellent.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a molding material according to an embodiment.

FIG. 2 is a cross-sectional view of a molding die showing a hot molding state of a piston for an internal combustion engine according to an embodiment.

[Explanation of symbols]

 2 Mold main body 4 Upper mold (molding mold) 5 Lower mold 10 Molding material 11 Powder compact 12 Metal film for lubrication

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B22F 5/02 B30B 11/02 Z C23C 30/00 B

Claims (2)

[Claims] 1. A molding material is loaded into a molding die, and a molding die for molding the outer surface or the inner surface of the molding product is pressed against the molding material to plastically flow the molding material to a predetermined shape. In the hot forming method, the outer peripheral surface of the green compact of the metal powder is coated with a lubricating metal film having excellent ductility. 2. The hot forming method for a metal powder according to claim 1, wherein the forming material is a green compact of an Al alloy powder coated with a lubricating metal film by plating or thermal spraying.