JPH03185202A - Manufacture of cam shaft - Google Patents

Abstract

PURPOSE:To avoid a quenching crack and increase joining force by a shrinkage fit by preheating a cam lobe, which is made of a sintered alloy and contains a hollow part, fitting this lobe to a periphery of a shaft member, and then welding these items by means of a high-energy beam while they remain at a high temperature. CONSTITUTION:In manufacturing a cam shaft, a cam lobe 1, which is made of a sintered alloy and contains a hollow part 11 having a circular section, is preheated first. Next, the cam lobe 1, which was preheated, is fitted to a periphery of a cam shaft member 2 consisting of, for example, a steel tube. In addition, while the cam lobe 1 remains at a high temperature, end parts 12 on both sides of the cam lobe 1 are welded to the peripheral surface of the shaft member 2 by means of a high-energy beam. After this, both cam lobe 1 and shaft member 2 are slowly cooled to complete the cam shaft. With this contrivance, a sudden change of temperature of the cam lobe 1 can be avoided to prevent it from a quenching crack, and at the same time both cam lobe 1 and shaft member 2 can firmly be joined, utilizing a shrinkage-fit-effect.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for manufacturing a camshaft, and more particularly to a method for manufacturing a camshaft in which a cam lobe made of a sintered alloy is fitted onto the outer periphery of a shaft member. .

(Prior Art) As mentioned above, an engine camshaft in which a shaft member is fitted into a hollow part of a cam lobe made of a sintered alloy,
Practical efforts are being made to meet the recent demands for lighter weight and more valve-multiplied engines.

The above-mentioned camshaft has been manufactured by fitting a cam lobe having a hollow portion into a shaft member and then welding the cam lobe and the shaft member at room temperature.

However, when a cam lobe made of sintered alloy is welded to a shaft member at room temperature, residual stress increases due to the rapid heating during welding, resulting in quench cracking at the interface of the weld or inside the weld. There was a problem that this occurred.

Therefore, there is a need to prevent defects when welding a cam lobe made of a sintered alloy and a shaft member, that is, cracking of the cam lobe due to welding, and to ensure the strength of the camshaft. For this reason, as shown in Japanese Patent Application Laid-Open No. 56-136296, welding of the cam lobe made of a sintered alloy and the shaft member is avoided, and a pipe member made of steel is incorporated into the hollow part of the cam lobe, and the hollow part of the pipe member is A method of manufacturing a camshaft has been proposed in which a shaft member is assembled in a camshaft, and a cam lobe and a pipe member, and a pipe member and a shaft member are welded to each other.

This camshaft manufacturing method uses a pipe member made of steel to reduce the residual stress generated during welding by reducing the carbon content of the welded part.
The idea is to prevent cracking.

(Problem to be Solved by the Invention) However, when a pipe member is interposed between the cam lobe and the shaft member, in addition to welding the pipe member and the shaft member as described above, welding between the cam lobe and the pipe member becomes difficult. Since this is necessary, it is inevitable that the number of work steps and costs will increase due to the two-time welding process.

Furthermore, since the weight of the camshaft increases by incorporating the pipe member, there is also a problem in terms of weight reduction.

In view of the above, an object of the present invention is to prevent weld cracking of a cam lobe made of a sintered alloy without increasing the number of work steps or increasing costs.

(Means for Solving the Problem) In order to achieve the above object, the present invention attempts to weld the cam lobe under high temperature conditions to avoid rapid temperature changes in the cam lobe, thereby preventing weld cracking. It is something.

Specifically, the solution taken by the present invention is that after preheating a cam lobe made of a sintered alloy and having a hollow part, the cam lobe is fitted onto the outer periphery of a shaft member, and then, while the cam lobe is still in a high temperature state, The cam lobe and the shaft member are welded together using a high-energy beam.

(Function) With the above configuration, the cam lobe made of sintered alloy is preheated and the shaft member is welded to the cam lobe while the cam lobe is in a high temperature state. The residual stress at is not very large.

Further, the cam lobe expands due to preheating, fits into the shaft member when in an expanded state, and contracts when returning to room temperature, so the cam lobe strongly grips the shaft member at room temperature.

(Example) Hereinafter, an example of a method for manufacturing a camshaft A according to the present invention will be described based on the drawings.

First, a cam lobe 1 made of a sintered alloy and having a hollow section 11 of circular cross section as shown in FIG. 1 is prepared.

The sintered alloy of the cam lobe 1 is Fe, which has a high carbon content that satisfies the wear resistance required for the camshaft A, and contains, for example, 0.5% to 4.5% C by weight.
Cr-based materials are preferred, specifically 4% Cr, M
A sintered alloy consisting of o: 1.5%, P: 0.6%, C: 3%, and the balance is Fe is preferable.

Further, the inner diameter of the hollow portion 11 of the cam lobe 1 is
It is preferable to set the diameter L7 to be slightly smaller than the outer diameter of the shaft member 2 (see Fig. 2) to be fitted into the cam lobe 1. For example, the inner diameter of the cam lobe 1 is set to 0.
．． Set it 005mm smaller.

Next, the cam lobe 1 prepared as described above is preheated. In this case, as a preheating condition, it is preferable to heat the cam lobe 1 to a temperature in the range of 300°C to 600°C in a non-oxidizing atmosphere, specifically, to heat it to about 450°C in nitrogen gas or argon gas. is preferable. By heating in a non-oxidizing atmosphere in this way,
The cam lobe 1 made of a high carbon sintered alloy can be prevented from forming scale due to oxidation.

Next, as shown in FIG. 2, the cam lobe 1 is attached to a steel pipe (
It fits onto the outer periphery of the shaft member 2 made of STKM13A). In this case, since the inner diameter of the cam lobe 1 is slightly larger than the outer diameter of the shaft member 2 due to expansion due to preheating, the cam lobe 1 is smoothly fitted into the shaft member 2. In addition, for example, the cam lobe 1 is preheated to about 450°C.
The temperature drops to about 350°C after fitting.

Next, the cam lobe 1 is in a high temperature state, for example, from 200°C to 50°C.
At a temperature within the range of 0.degree. C., as shown in FIG. 3, both end portions 12, 12 of the cam lobe 1 and the outer peripheral surface of the shaft member 2 are welded using a high energy beam, such as a laser beam or an electron beam. In this case, when welding with a laser beam, Dekani 2KW is preferable.

In the above case, the temperature condition of the cam lobe 1 is set to 200°C to 500°C.
The reason for setting it in the range of ℃ is as follows. That is, if the temperature of the cam lobe 1 during welding is less than 200°C, the temperature difference before and after welding is too large, which may cause quench cracking due to welding. If the welding temperature is exceeded, scale may be generated due to oxidation of the cam lobe 1, which may become involved during welding, and the cam lobe 1 may be softened, resulting in a decrease in hardness or strength. be.

For this reason, the cam lobe 1 is set to 30 mm as described above.
Preheat to a temperature of 0°C to 600°C, and 20°C during welding.
When maintained at a high temperature of 0° C. to 500° C., the cam lobe 1 is not rapidly cooled even when heated by welding, so a sudden temperature change is avoided, residual stress is relaxed, and quench cracking does not occur.

Next, the welded cam lobe 1 and shaft member 2 are slowly cooled to obtain a camshaft A as shown in FIG. 4.

When the camshaft A is obtained as described above, the cam lobe 1 expanded by preheating is slowly cooled and contracts when returning to room temperature, so the bonding force between the cam lobe 1 and the shaft member 2 is improved by the shrink fit effect. .

(Effects of the Invention) As explained above, according to the method for manufacturing a camshaft according to the present invention, the cam lobe made of a sintered alloy is welded to the shaft member in a high temperature state, so the cam lobe does not need to be heated during welding. Since sudden temperature changes are avoided and residual stress does not increase, quench cracking can be reliably prevented.

In addition, the cam lobe is preheated and expanded, and then contracts when returning to room temperature, so that it strongly grips the fitted shaft member during expansion due to the shrink fit effect, thereby improving the bonding force.

[Brief explanation of drawings]

1 to 4 each show a method of manufacturing a camshaft according to an embodiment of the present invention, and FIG. 1 is a longitudinal cross-sectional view of a cam lobe;
FIG. 2 is a longitudinal sectional view of the fitting process of the cam lobe to the shaft member, FIG. 3 is a longitudinal sectional view of the welding process of the cam lobe and the shaft member, and FIG. 4 is a front view of the annealing process. A...Camshaft 1...Cam lobe 2...Shaft member 11...Hollow part A...Camshaft diagram diagram diagram diagram diagram

Claims (1)

[Claims] (1) After preheating a cam lobe made of a sintered alloy and having a hollow part, the cam lobe is fitted onto the outer periphery of the shaft member, and then, while the cam lobe is in a high temperature state, the cam lobe and the shaft member are heated to a high temperature. A method for manufacturing a camshaft characterized by welding using an energy beam.