JP2002194404A - Method for manufacturing engine valve, and engine valve - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an engine valve by which the breakage of the shank of a powder compact before sintering can be prevented and productivity can be improved and also to provide the engine valve. SOLUTION: This manufacturing method comprises: a step where, in a state in which an end part of a hard shank 1 made of titanium alloy is inserted in titanium-alloy powder, the titanium-alloy powder is compacted into a short columnar shape; a step where the resultant powder compact 2 with the hard shank 1 is sintered; and a step where a sintered body 7 part of the powder compact 2 after the sintering is subjected to upset forging together with the end part of the hard shank 1 to form a valve head 5 integrated with the hard shank 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an engine valve used as an intake valve or an exhaust valve in an internal combustion engine, and more particularly to a method of manufacturing a titanium alloy engine valve and an engine valve.

[0002]

2. Description of the Related Art For example, a forged product using heat-resistant steel has been generally used as an engine valve of an automobile.
Recently, development of a titanium alloy engine valve has been promoted because of its light weight and excellent heat resistance and strength.
As a method of manufacturing this titanium alloy engine valve, a powder metallurgy method of sintering titanium alloy powder is excellent in terms of the degree of freedom in controlling the composition of the material and the manufacturing cost, and has been put to practical use. I have.

In this powder metallurgy method, it is necessary to form a powder as a first step, and a common cold isostatic pressure (CIP) molding method is a molding method using a rubber mold or a hydraulic pressure because of the use of a rubber mold or water pressure. Since the molding process is complicated and unsuitable for mass-produced engine valves, conventionally, as shown in FIG. 6, a stepped shaft-shaped die 30 is set on a press machine such as a hydraulic press or a mechanical press. The titanium alloy powder 32 accommodated in the molding space 31 is vertically compressed by a punch 33 and a counter punch 34 to obtain a stepped shaft-shaped powder compact 35 having a short cylindrical head. As shown in the drawings, after sintering in the next step, a method of upsetting and forging the head of the sintered body 36 to obtain an engine valve material 38 having a valve head 37 has been attempted.

However, in the powder compact 35, as shown in FIG. 5, since the L (length) / D (diameter) of the compact is as large as 7 or more, the powder density near the center in the vertical direction is sufficiently high. The shaft 35a of the powder compact 35 was damaged during handling (hereinafter referred to as "handling") such as gripping, transporting, setting to a sintering device, etc., from the release from the die 30 to sintering, without improvement. Therefore, there is a large problem that the production line of the engine valve is frequently stopped.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems, and it is possible to prevent a shaft portion of a powder molded product before sintering from being damaged, thereby improving productivity. An object of the present invention is to provide a method of manufacturing an engine valve and an engine valve.

[0006]

In order to achieve the above object, the present invention provides a method of manufacturing an engine valve, comprising the steps of: A step of compression-molding the powder into a short columnar shape, a step of sintering the obtained powder compact with a hard shaft, and a step of sintering the sintered compact of the powder compact with the hard shaft. Forming a valve head integral with the hard shaft by upsetting and forging with the tip. An engine valve according to the present invention is manufactured by the above manufacturing method.

In the present invention, a titanium alloy hard shaft is a rod or a rod of a titanium alloy, which is an ingot obtained by rolling or drawing a titanium alloy ingot, or a powder formed by molding a titanium alloy powder into a rod. A sintered body obtained by sintering the body,
And a temporary sintered body obtained by sintering the powder compact for a short time.

According to the present invention, the powder molded product before sintering is composed of a powder molded product with a hard shaft. The shaft is not damaged, and high-speed handling can be performed without any trouble.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In the method of manufacturing an engine valve according to the present invention, as shown in FIG. 1, a titanium alloy powder is compression-molded to form a powder compact 2 having a hard shaft 1 made of titanium alloy.
And a step of sintering the same, and a step of hot-swaging and forging the head of the obtained sintered insert 4 to form the valve head 5. Having.

First, in the compression molding, as shown in FIG. 2, a die 10 having a short columnar molding space 12 and a shaft hole 13 and a spacer 11 (a die in which both are integrated) may be used as a holder 14. The steel lower mold 15 incorporated in the
It is set on a press machine such as a hydraulic press or a mechanical press (not shown), and a hard shaft 1 made of a titanium alloy and having a predetermined length is fitted into the shaft hole 13 with a small clearance. The lower end of the hard shaft 1 is supported by a counter punch 16 in a state where the hard shaft 1 is protruded by a predetermined length, the titanium alloy powder 6 is filled in the molding space 12, and compressed downward by a steel punch 17, A powder compact 2 compacted into a short cylinder is formed.

As a result, the hard shaft 1 is insert-molded integrally with the powder compact 2 and the L / D of the powder compact 2 is a small value of about 2, so that the titanium alloy powder is uniformly compressed at a high density and hardened. The resulting powder compact 2 with the hard shaft 1 is firmly fixed to the tip 1a of the shaft 1.
Even if the hard shaft 1 is gripped and conveyed by a robot hand or the like, the insert molded product 3 made of is not damaged, and the high-speed handling can be performed without any trouble.

In the next step, the insert molded product 3 is sintered by a conventional method to form an insert sintered product 4 in which the hard shaft 1 and the sintered compact 7 of the powder compact 2 are integrated. Next, after the insert sintered product 4 is heated, the mold 1 of the hot forging machine is heated.
8, and 7 parts of the sintered body are upset-forged together with the tip 1 a of the hard shaft 1 by pressing down the punch 19, and the valve head 5
Is formed to obtain an engine valve material 8 having a valve head 5 integrated with the hard shaft 1.

As shown in FIG. 1 and FIG. 3 showing an embodiment to be described later, the tip portion 1a of the hard shaft 1 is deformed by the upsetting forging so as to expand and expand in the diameter direction. Since the collar portion 1c is formed, and the forged structure 9 of the sintered body forming the valve head portion 5 in a form including the collar portion 1c is solidified, the valve head portion 5 is firmly connected to the hard shaft 1. During integration and use in the engine as a post-process and as an engine valve product, the hard shaft 1 and the valve head 5 do not come off, and excellent joining strength and fatigue strength can be obtained.

The engine valve blank 8 obtained by the upsetting forging described above is subjected to mechanical processing such as grinding by a conventional method after correcting the linearity of one portion of the hard shaft as required, thereby obtaining an engine valve product.

In the above process, the hard shaft 1 made of titanium alloy is used.
The material of the titanium alloy powder 6 is, for example, Ti-6Al- in the case of an engine valve used as an intake valve.
In the case of an engine valve using a 4V alloy and used as an exhaust valve exposed to a higher temperature, a high heat resistant Ti-6 is used.
Various Ti alloys can be selected and used depending on the use, such as using an Al-2Sn-4Zr-2Mo alloy. Further, the hard shaft 1 and the titanium alloy powder 6 for forming the valve head 5 are made of different materials. Those can also be used.

As described above, the hard shaft 1 made of a titanium alloy can be made of various types of rods or wires depending on the material, such as an ingot of a titanium alloy, a sintered product or a temporarily sintered product of a rod-shaped compact of a titanium alloy powder. What cut | disconnected or shape | molded the shape to predetermined length can be used. In addition, the above-mentioned temporary sintering product is the same as the normal sintering at the same sintering temperature, only the sintering time is shortened (for example, the normal sintering time = 4 hours, = 30 minutes), and the density of the sintered product is about 90-99% in the case of normal sintering,
Although the density of the pre-sintered product is about 80%, even if this pre-sintered product is used as the hard shaft 1, a sufficient bending strength can be obtained that can prevent the insert molded product 3 from being damaged during handling. Things.

[0017]

EXAMPLE A hard shaft 1 was prepared by cutting a wire having a diameter of 5.8 mm, which is an ingot of Ti-6Al-4V alloy, to a length of 115 mm, and a titanium alloy powder 6 was made of an alloy powder of the same material as above. It is compression-molded by a mechanical press having a compression stroke of 15 mm in which the steel die 10 and the spacer 11 of FIG. 2 are set, and D = 16.6 mm, L = 3
Forming a powder compact 2 of 3.2 mm (L / D = 2.0);
An insert molded product 3 in which the tip of the hard shaft 1 was inserted by about 15 mm was obtained. The insert molded product 3 is anoxic by purging air with an inert gas and further sintered at 1300 ° C. for 120 minutes in a vacuum atmosphere. After heating the body 7 and the tip portion 1a to 1100 ° C., it was upset forged by a hot forging machine to obtain an engine valve blank 8 having a valve head portion 5 having a diameter of 30 mm.

The shaft of the insert molded product 3 is a hard shaft 1
Therefore, the handling of the engine valve blank 8 during the period from demolding to sintering was performed at a high speed without any trouble. Further, the hard shaft 1 and the valve head 5 are firmly integrated, and the valve head 5 of the engine valve material 8 is cut vertically and the cut surface is observed by means of grain flow photography, as shown in FIG. Material flow during forging and tip 1 of hard shaft 1
a is observed, the tip 1a has a diameter of about 12 mm
The formation of the brim-like portion 1c was observed.

The present invention is not limited to the above-described example. For example, the materials of the hard shaft 1 and the titanium alloy powder 6 and the heating temperature during sintering and forging may be other than those described above. The tip portion 1a of the hard shaft 1 may be formed in a straight rod shape as described above, or may be one in which an outer diameter portion is provided with rib-like irregularities in advance.

As a molding die for powder compression molding for obtaining the insert molded product 3, in addition to a molding die shown in FIG. 2 which is made of steel, a rubber molding die having a molding space 12 as shown in FIG. Using a die 20 and a punch 21 in which a rubber pressing body 21b is attached to the tip of a steel punch body 21a, a molding die 22 for compression molding the titanium alloy powder 6 may be used. By the compression deformation of the rubber die 20, the titanium alloy powder 6 can be sealed so as not to enter the gap between the hard shaft 1 and the shaft hole 13 of the spacer 11, and the shaft hole 13 can be cleaned at the end of the molding process. This has the advantage that it becomes unnecessary. In the figure, the same parts as those in FIG.

[0021]

As described above, according to the present invention,
Since the shaft of the powder molded product before sintering consists of a hard shaft, the shaft does not break during handling such as gripping and transporting from demolding after sintering to sintering. Since the stoppage of the production line is eliminated and the time from demolding to sintering can be shortened by high-speed handling,
The productivity of the production of an engine valve by the powder metallurgy method can be improved.

[Brief description of the drawings]

FIG. 1 is a process chart showing a method for manufacturing an engine valve of the present invention.

FIG. 2 is a longitudinal sectional view of a molding die showing a compression molding step in FIG.

FIG. 3 is an enlarged vertical sectional view of a valve head portion of an engine valve raw material obtained according to the present invention.

FIG. 4 is a longitudinal sectional view showing another embodiment of the molding die used in the compression molding step in the method for producing an engine bubble of the present invention.

FIG. 5 is a process chart showing a conventional method for manufacturing an engine valve.

FIG. 6 is a longitudinal sectional view of a mold part showing a compression molding step in FIG. 4;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Hard shaft, 1a ... Tip part, 2 ... Powder compact, 5 ... Valve head part, 6 ... Titanium alloy powder, 7 ... Sintered body, 8 ... Engine valve material, 10 ... Dies, 12 ... Molding space, 17 ... Punch, 18 ... Mold, 19 ... Punch, 20 ... Dice, 21 ...
punch.

Claims (2)

[Claims] 1. A step of compression-molding the titanium alloy powder into a short column while inserting the tip of the titanium alloy hard shaft into the titanium alloy powder, and forming the powder with the obtained hard shaft. A step of sintering the body, and a step of upsetting and forging the sintered body of the powder compact after the sintering together with the tip of the hard shaft to form a valve head integral with the hard shaft. A method for manufacturing an engine valve, comprising: 2. An engine valve manufactured by the manufacturing method according to claim 1.