JPS6220859A - Production of poppet valve - Google Patents

Abstract

PURPOSE:To improve the durability of an engine valve by partly melting the Ti alloy engine valve by local heating then quickly cooling the valve so that the melted part is made amorphous and is hardened. CONSTITUTION:One end of a round stock made of a Ti-6Al-4V Ti alloy is made by up setting into a ball shape and is further forged to form a bevel part 2. The stock is subjected to a heat treatment then to necessary machining. A stem end face 5 is preliminary cut substantially to a finish size except at allowance for finishing. the surface of the poppet valve formed in the above- mentioned manner is heated by a laser and is quickly cooled with water so that the material is made amorphous to have high hardness; thereafter, the surface layer is finished by polishing. The surface of the valve stem part 1 is hardened by nitriding, oxidation, plating etc. A face 4 and stem end face 5 of the engine valve which are liable to wear are made to the amorphous structure having the high hardness, by which the durability of the Ti alloy engine valve is improved.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing a mushroom-shaped titanium alloy valve.

[Conventional technology]

FIG. 4 shows an example of a conventional titanium alloy engine valve. In the figure, 1 is the valve stem.

2 is a valve head portion, and 3 is a shaft end tip. The valve stem portion 1 and the valve head portion 2 are made of a titanium alloy Ti-(3At-4V, etc.), and the end of the valve stem portion 1 is made of a Co-based heat-resistant and wear-resistant alloy (stellite) to improve wear resistance. The shaft end tip 3 is brazed.

Further, the outer peripheral surface of the valve is subjected to surface hardening treatments such as nitriding and chrome plating.

[Problems to be solved by the invention]

However, the above conventional method has the following problems.

(1) When titanium alloys are used as mechanical parts, sliding parts tend to seize, and parts subject to friction tend to wear out.

In the above-mentioned conventional valve, the tip 3 of a CO-based heat-resistant and wear-resistant alloy is entirely brazed to the shaft end face of a titanium alloy engine valve in order to improve wear resistance.

This requires precise pre-machining of CO-based heat-resistant and wear-resistant alloys and titanium alloys, which are difficult-to-cut materials, and further requires brazing the tips, making the valve extremely expensive.

(2) In an engine valve, the face surface 4 and the shaft end surface 5 are mating members (valve seats).

(tabet scree, etc.), and when in contact, friction occurs under high surface pressure, so wear resistance is required.

Even if surface hardening is applied to titanium alloy engine valves, if the hardened layer is thin, it will easily wear out.

Conventionally, there has been no low-cost and effective measure to improve the wear resistance of the face surface 4 of the umbrella portion 2, which is a factor that reduces the durability of this type of titanium alloy engine valve.

The present invention has been made in view of the above, and an object of the present invention is to provide a mushroom-shaped valve made of a titanium alloy that is low in cost and wear-resistant.

[Means for solving the problem 2] When a titanium alloy is rapidly cooled from a molten state, it solidifies without forming metal crystals.

This solidified phase is called an amorphous phase, and this phase is hard and brittle.

Therefore, the present invention is characterized in that required portions of the titanium alloy mushroom-shaped valve are melted to a required depth and then rapidly cooled to provide the required wear resistance.

〔Example〕

One embodiment of the present invention will be described below with reference to FIGS. 1 to 3. Reference numeral 1 indicates a valve stem.

2 is the valve head portion, 4 is the face surface of the valve head portion 1, and 5 is the valve stem portion 1.
This is the shaft end face of

The mushroom-shaped valve is made of a titanium alloy (Ti-6At-4v titanium alloy...6% by weight of At, 4% by weight of V).

90% by weight of Ti.

A method for manufacturing the above mushroom-shaped valve will be explained.

(1) Pre-partial hardening process: One end of the round bar material is forged into a ball shape, and further forged to form the umbrella part. Next, heat treatment is performed, followed by necessary machining.

At this time, the shaft end face 5 is cut to the finished dimensions, leaving a finishing allowance.

(2) Partial hardening: Partial hardening is performed on the shaft end surface 5 and face surface 4. Details of the partial curing are as follows. After the surface of the titanium alloy mushroom-shaped valve is heated by laser and melted (melting point 1540-1
650°C) and quenched with water. When a molten titanium alloy is rapidly cooled and solidified, it solidifies without being able to grow crystals, so it becomes amorphous (non-crystalline), which does not have the original metal crystals. In an amorphous material, metal elements do not form crystals but are arranged in a disordered manner, resulting in a hard and brittle material due to interstitial strain. Due to this.

You can harden the necessary areas to the appropriate depth.

(3) Finishing: Since the surface of the partially hardened part is rough, the second surface layer is finished by polishing.

(4) Surface treatment: Face surface 4. Although the shaft end face 5 was hardened.

If the valve stem 1 is left unhardened, there is a risk of seizure due to sliding with the valve guide, so a surface hardening treatment is applied to the outer periphery of the valve stem 1. Treatment methods include nitriding, oxidation, plating, etc.

As described above, the present invention is achieved by locally heating and melting a part of a titanium alloy engine valve using a laser or the like, and then rapidly cooling it with water.

The portion is made amorphous and hardened. In an engine valve, the face surface 4 and the shaft end surface 5 are prone to wear, so these two parts are hardened to improve the durability of the engine valve made of titanium alloy.

FIGS. 2 and 3 show other embodiments of the invention. In the case of FIG. 2, the valve head portion 2 and the valve stem portion 1a.

1b is made separately from a different titanium alloy material.

Welding is done at parts A, B, and C. In the case of FIG. 3, after the valve head portion is made of a titanium alloy valve base material, the face portion of the valve head portion 2 and the shaft end portion of the valve stem portion 1 are made amorphous.

[Effects of the Invention] The present invention is constructed as described above, and the present invention has the following effects.

The shaft end surface of a titanium alloy mushroom valve.

By hardening parts that require wear resistance, such as the face, the durability of the valve can be improved. Furthermore, since the base material of the valve is only heated and rapidly cooled, the valve can be manufactured at low cost.

[Brief explanation of drawings]

1 to 3 are external views showing three embodiments of the present invention, and FIG. 4 is an external view showing a conventional example. 1... Valve stem portion, 2... Valve head portion, 4... Face surface. 5... Shaft end surface. 4 Mane Notification 3Z

Claims (1)

[Claims] A method for manufacturing a mushroom-shaped valve made of a titanium alloy, which comprises heating a portion of the mushroom-shaped valve and then rapidly cooling it to make the portion amorphous (non-crystalline).