JPH08284943A - Manufacture of hot-forged article - Google Patents

Abstract

PURPOSE: To enable the manufacture of a forget article provided with mechanical charactersitics not inferior to conventional ones even if they are not heat- treated after forging processing by performing hot forging, using non-heat treated steel as material. CONSTITUTION: Non-heat treated steel of, for example, HRC 23-28 is prepared as a material. The material consisting of non-heat treated steel is cut into desired size, and then the part 3a to be forged, which serves as a crank arm, is heat-treated to a high temperature of, for example, 1200 deg.C or thereabouts by a fixed electrode 6 and a mobile electrode 7 for electric resistance heating. At the same time, a part of the crack arm is preliminarily molded by charging specified pressure P in axial direction from the side on the nonheating side to the part 3a to be forged against the heat-resistant fixed electrode 6 bearing the part 3a. Next, hot forging main molding is performed for the part 3a to be forged, using an up center, whereby the shape of the part of the crank arm is obtained. Then, aftertreatment such as burr removal, etc., is performed, and then it is cooled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a hot forged product, and is particularly suitable for manufacturing a small and lightweight crankshaft of an internal combustion engine used as a prime mover of a portable working machine or the like. It is a technology.

[0002]

2. Description of the Related Art For example, in manufacturing a hot forged product such as a crankshaft, a material such as S43 is generally used.
Carbon steel such as C was used. Then, through a cutting step and a heating step, forging is performed by an appropriate method, followed by cooling, and finally heat treatment to obtain desired mechanical properties.

However, as shown in FIG. 3, carbon steel has a drawback that the quenching method is difficult because it is easily affected by the mass effect. In recent years, carbon steel is heated to a predetermined temperature and then left to cool in the air to a predetermined mechanical strength. Although a non-heat treated steel that can obtain properties has been used, it has a drawback that the impact value is lower than that of the heat treated steel.

[0004]

The present invention simplifies the manufacturing process in the conventional general manufacturing method as described above,
Moreover, it is an object of the present invention to provide a novel method capable of obtaining a hot forged product having mechanical properties comparable to those of conventional products.

[0005]

In order to solve the above problems, the method for manufacturing a hot forged product according to the present invention is to perform hot forging by using non-heat treated steel as a raw material.

It is also possible to use non-heat treated steel as a raw material and partially heat the raw material to hot forge the heated portion.

[0007]

In the method of the present invention, non-heat treated steel is used as a raw material in place of the generally used heat treated steel.

As a result, a forged product having mechanical properties comparable to those of conventional products could be manufactured without heat treatment after the forging process.

[0009]

EXAMPLES Examples of the method of the present invention will be described below.

Now, for example, a crankshaft 1 of a small and lightweight internal combustion engine used as a prime mover of a portable work machine or the like.
Consider the case of manufacturing (see FIG. 2). In manufacturing such a crankshaft 1, in addition to the method of integrally forming the crankpin 2, the crank arm 3, and the shaft portion 4 from the beginning, from the viewpoint of simplifying the molding, the shaft portion 4 and the crank A method is known in which only the arm 3 is integrally formed with each other, and the arm 3 is joined to a separately formed crank pin 2 to manufacture the crankshaft 1 in an assembled manner.

Therefore, an embodiment of the method of the present invention will be described by taking as an example the case of molding an integral product 5 of the shaft portion 4 and the crank arm 3 in the assembled crankshaft.

<First Example> The first example is a case where hot cutting is performed by heating the entire cut material.

First, as a material, unlike the case of the conventional general hot forging method, for example, non-heat treated steel of HRC23 to 28 is prepared. The heat-treated steel used in the conventional method has a sorbite structure, whereas the non-heat-treated steel used in this example has a ferrite-pearlite structure. This pearlite structure is similar in mechanical properties to the sorbite structure of conventional heat-treated steel, and is a ferrite-pearlite structure in which vanadium carbide is precipitated in a ferrite structure that is significantly inferior in mechanical properties to the sorbite structure. As a result, it is possible to obtain mechanical properties comparable to those of heat-treated steel.

A material made of such a non-heat treated steel is cut (cutting step) into a desired size, and then a heavy oil furnace, an electric furnace,
In an appropriate heating furnace such as a high frequency furnace, the whole is heated to a high temperature of, for example, about 1200 ° C (heating step).

Next, hot forging is performed by using an appropriate forging machine according to a predetermined forging method such as various free forging methods and die forging methods (forging step), and the shaft portion 4 of the crankshaft 1 is The shapes of the part and the part of the crank arm 3 are given.

The details of the cutting step, the heating step and the forging step are the same as those of the conventionally known manufacturing method.

After that, if necessary, post-processing such as deburring and straightening is performed, and then cooled (cooling step).

In this embodiment, in cooling, not only intentional cooling such as air cooling or water cooling is eliminated, but even if it is unintentional, it is contacted with the forced air flow. Be careful to let it cool naturally, without doing so. For example, at a hot forging work site, a fan or the like is arranged to protect a worker from high temperatures. The wind of such an electric fan normally hits not only the worker but also the forged product unintentionally. In this embodiment, the forged product is naturally cooled in the atmosphere while being protected from contact with such unintentional air flow.

The reason will be described. The shaft portion 4 of the crankshaft 1 in this embodiment has a small diameter, for example, about 8 to 12 mm. For this reason, even if the wind of the fan is touched, the forced cooling action may be exerted, and the quality may change unexpectedly. Therefore, care must be taken so that even if the amount is small, the forced air flow does not hit the forged product.

As a specific means, for example, when the forged product becomes around 600 ° C at which the color of the forged product disappears, the forged product is placed in a metal container having an open upper part and left as it is. And wait for it to cool. Since the side wall of the container blocks the forced air flow by the fan or the like, the forced air flow is prevented from coming into contact with the forged product in the container.

If the forged product is large enough so that its quality does not change even when exposed to cooling air, it is not necessary to take the above special consideration in the cooling process, and the same method as the conventional method is used. It may be cooled by cooling.

Finally, the surface of the forged product is cleaned by shot blasting or the like. The heat treatment step after the cooling step, which is required in the conventional method, is unnecessary.

The hot forged product obtained through the above steps has a hardness of HRC23 to 28 and a small amount of coarse crystal grains.
Both hardness and tenacity were comparable to those of forged products obtained by conventional methods.

According to the manufacturing method of this embodiment, it is possible to omit the heat treatment step after cooling, which has been conventionally indispensable, and to provide a hot forged product having mechanical properties comparable to those of conventional products. can get.

<Second Embodiment> The second embodiment is a case where a part of the cut material is partially heated and hot forging is performed on this heated part. As a material, for example, HRC23-
The use of 28 non-heat treated steel is the same as in the first embodiment.

A material made of non-heat treated steel is cut into a desired size (cutting step) and then preformed while heating a part of the material (forged portion to be forged) (heating / forging preforming step). .

Specifically, for example, as shown in FIG. 1, the forged portion 3a (specifically, the crank arm 3 and the crank arm 3) of the same material as the first embodiment having a diameter of 8 to 12 mm that is cut. The fixed electrode 6 and the movable electrode 7 are arranged so as to electrically resistance-heat the above-mentioned (for
Is heated to a high temperature of about 1200 ° C., for example.
At the same time, a predetermined pressure P is applied in the axial direction from the end on the non-heated side, and the forged portion 3a is pressed against the heat-resistant fixed electrode 6 that receives the portion 3a, whereby the crank arm 3 is pressed. Preform the part of.

Then, hot forging main forming is performed on the forged portion 3a requiring forging by using, for example, an upsetter,
The shape of the crank arm 3 is obtained (forging main forming step). The portion 4a corresponding to the shaft portion 4 of the crankshaft 1 is not heated and is left linearly in its original shape.

After that, if necessary, post-treatment such as deburring and straightening is performed, and cooling is performed (cooling step). This cooling process is performed in the same manner as in the first embodiment.

Finally, the surface of the forged product is cleaned by shot blasting or the like. The heat treatment step after cooling, which was required in the conventional method, is unnecessary.

The forged product obtained through the above steps has a hardness of HRC23 to 28 (heat-affected zone is HRC20 to 23).
The hardness and tenacity were comparable to those of the forged products obtained by the conventional method.

According to the method of heating only a part of the cut material and forging the heated portion like the method according to the present embodiment, the forged product inevitably has a temperature rising portion. A thermal boundary with the room temperature remains. The metal structure of the thermal boundary part is an intermediate structure between the heated part and the non-heated part. Therefore, according to the traditional tradition of the past, it was necessary to eliminate the thermal boundary and to homogenize the metallographic structure by means such as repeatedly performing heat treatment after cooling.

On the other hand, in the manufacturing method according to this embodiment, the heat treatment step for eliminating the thermal boundary portion is not provided. This is because, with the progress of steelmaking technology in Japan, it has become possible to obtain high-quality steel products containing almost no impurities, and if such high-quality steel products are used as raw materials, the thermal boundary part will remain in the forged product. It is based on the new recognition that mechanical properties comparable to conventional products can be guaranteed even if they are left as they are.

According to the manufacturing method of this embodiment, as in the first embodiment, the heat treatment step after cooling, which has been heretofore indispensable, can be omitted, and the mechanical strength is not inferior to the conventional product. A hot forged product with properties can be obtained.

The manufacturing method according to the second embodiment requires a relatively long time from the introduction of raw materials to the completion, as compared with the manufacturing method according to the first embodiment. However, the method of the second embodiment is also suitable for high-mix low-volume production, which is the mainstream of today's production methods, because the setup change time is short.

Further, according to the forged product obtained by the method according to the second embodiment, there is an advantage that, when the forged product is put into the machining process after the cooling process, the occurrence of troubles in the machining process is small. .

That is, in the case of die-forging the integral product 5 of the shaft portion 4 and the crank arm 3 after heating the whole cut material, considering the ease of removal from the die,
It is common to use a mold that is formed so that the shaft portion has a taper. Conventionally, when an integrated product of a shaft portion and a crank arm obtained in this way is put into the machining process of an automatic line, since a taper is formed in a portion that becomes the shaft portion 4, It was easy to cause damage.

In this respect, according to the method of the second embodiment,
It is not necessary to form a taper on the portion 4a that serves as the shaft portion of the crankshaft 1, and the portion 4a corresponding to the shaft portion 4 can be left linearly in the original shape of the material. For this reason, there is no problem such as failure to grab in the machining process with an automatic line, no trouble occurs, and there is no need to delete the taper part, so there is little loss of processing cost and material cost and it is rational. Target.

The non-heat treated steel shaft treated by the method of the present invention as described above was subjected to 3000 r based on the ANSI test method.
Repeated impact tests were carried out on the shaft of the impeller rotating at pm and no cracks were observed.

[0040]

EFFECTS OF THE INVENTION According to the present invention, the heat treatment step after cooling, which was conventionally indispensable, can be omitted, and moreover,
A hot forged product having mechanical properties comparable to conventional products can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a heating / forging preforming step in a manufacturing method according to an embodiment of the present invention.

FIG. 2 is a front view showing an assembled crankshaft as an example of a forged product obtained by the method of the present invention.

FIG. 3 is a hardness comparison diagram showing heat treatment properties of heat-treated steel and non-heat-treated steel.

[Explanation of symbols]

 3a Forging process required 6 Fixed electrode 7 Movable electrode

Claims (2)

[Claims] 1. A method for manufacturing a hot forged product, characterized in that hot forging is performed using non-heat treated steel as a raw material. 2. A method for producing a hot forged product, characterized in that non-heat treated steel is used as a raw material, and a part of the raw material is partially heated to hot forge the heated portion.