JP2820355B2 - Manufacturing method of forged parts with excellent vibration damping - Google Patents

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 forged part requiring high strength and vibration damping.

[0002]

2. Description of the Related Art In recent years, many automotive parts have been required to have an added value of vibration damping in addition to strength and toughness that can withstand fatigue and wear. In other words, as luxury vehicles become more advanced, there is a strong need for high-strength, high-damping components that reduce vibration and noise due to engine operation or vibration due to uneven road surfaces during driving and realize comfortable driving. .

In view of the above background, the gear is divided into two layers, an outer part made of spheroidal graphite cast iron and an inner part made of flaky graphite cast iron.
Japanese Patent Laid-Open Publication No. 2-107721 discloses a manufacturing method for fitting and integrating, and a method of press-fitting after inserting an anti-vibration metal body between the outer periphery of the gear material and the inner periphery of the annular tooth member by press-fitting or casting. The production method is disclosed in JP-B-59-39217.

Further, the present inventors have disclosed in Japanese Patent Application No. 03-140.
No. 275 proposes a composite molten forging method in which a metal body having a lower melting point than a hollow body made of a steel material is inserted into a hollow body made of steel, and these are heated to melt only the metal body.

[0005]

However, all of these methods have the following problems. That is, Japanese Patent Application Laid-Open No. 2-107721 has problems of cost increase and reliability of the fitting portion due to an increase in man-hours.
No. 17 has a problem of cost increase due to an increase in man-hours, and none of these methods can be used for manufacturing parts other than gears. Japanese Patent Application No. 03-140275
The issue does not take damping properties into account. The present invention has been made in view of the above circumstances, and provides a method of accurately forming a part having a sufficient strength in an outer layer and a sufficient damping property in an inner layer by a single forging.

[0006]

According to the present invention, a graphite cast iron or alloy cast iron having excellent vibration damping properties is inserted into a hollow body, and the melting point of the metal body is set at -50 ° C. as a lower limit. After performing high-frequency heating with the melting point of −20 ° C. as the upper limit, the oxide film on the surface of the hollow body is removed, and then molded and integrated in a preheated mold. As a result, the surface forging has high strength, the inside has excellent vibration damping properties, the conventional workability is secured, the formation of an oxide film on the surface of the hollow body is suppressed, and the composite forging has excellent surface properties. Parts can be realized. That is, the gist of the present invention is as follows: (1) A steel material having a carbon content of 0.1% or more and less than 2% by weight is formed in advance into a simpler shape than the product shape, and its thickness is After inserting graphite cast iron, gray cast iron or alloy cast iron having excellent vibration damping properties into a hollow body having an outer diameter ratio of 0.20 or less, the melting point of the inserted metal body −
After high-frequency heating at an average heating rate of 5 ° C./sec or more and 20 ° C./sec or less in a temperature range having a lower limit of 50 ° C. and an upper limit of the melting point of the hollow body −20 ° C., the oxide film is removed and inserted. 200 ° C while the metal body is in a molten or semi-molten state
The above average 200 mm /
A method for producing a forged part having excellent vibration damping characteristics, wherein the forged part is formed by pressurizing at a processing speed of not less than a second, forming the product into a product shape, and solidifying the product. (2) The method of the above (1), wherein after the main forming, at the bottom dead center at the time of forging, a load of 30% or more of the maximum load at the time of forging is maintained until the surface temperature of the hollow body becomes 800 ° C. or less. It is in.

[0007]

FIG. 1 shows an embodiment of a forging method according to the present invention. In FIG. 1A, a hollow body 1 made of a steel material having a carbon content of less than 2% and having a wall thickness / outermost diameter ratio of 0.20 or less is formed into a simpler shape than the product shape. A metal body 2 having excellent vibration damping properties is inserted in advance, and heating is performed in the high-frequency heating coil 3 with the lower limit of the melting point of the metal body −50 ° C. and the upper limit of the melting point of the hollow body −20 ° C.
As a result, only the inserted metal body is melted, and the hollow body can maintain its shape and secure the same workability as that of the conventional hot forging. Thereafter, as shown in FIG. 1B, the oxide film on the surface layer of the hollow body is removed by the oxide film removing device 4. Thereafter, these are inserted into the mold 5 and, as shown in FIG. 3 (c), in a mold preheated to 200 ° C. or higher by a heating device 8 such as high-frequency heating, with a punch 6 at an average speed of 200 mm / sec or more. Perform molding. This allows
The void 7 is filled with the hollow body and the molten metal body, and the product 9 is completed.

[0008] The reason why the carbon content of the steel material used for the hollow body is 0.1% or more and less than 2% is that if less than 0.1%, the deformation resistance during cold is low, so that the deformation resistance is reduced by heating. This is because there is no effect, and a steel material having a carbon content of 2% or more has low ductility, the hollow body is damaged at the time of press forming, and the molten inserted metal body flows out. The reason why the thickness / maximum diameter ratio of the hollow body is set to 0.20 or less is that the thickness / maximum thickness exceeds this.
This is because the hollow body having the outermost diameter ratio is less likely to fill the void 6 in the mold during the subsequent pressure molding, and cannot be molded into a product shape.

The metal body to be inserted into the hollow body is graphite cast iron, gray cast iron or alloy cast iron because these metals have excellent vibration damping properties. The lower limit of the heating temperature is the melting point of the metal body −50 ° C. because the inserted metal body does not melt at a lower temperature. The upper limit of the heating temperature is the melting point of the hollow body −20 ° C., because at a temperature higher than this, the hollow body may melt and may not be forged.

The reason why high-frequency heating is used to reduce skin roughness due to oxidation during heating, and the heating rate at that time is set to 5 ° C./sec or more, is to suppress uniform heating of the hollow body and generation of an oxide film. . The reason why the heating rate is set to 20 ° C./sec or less is that if the heating rate is exceeded, the internal temperature of the hollow body becomes non-uniform, and there is a possibility that the hollow body will melt off locally. Note that heating in an atmosphere of an inert gas such as argon or nitrogen is also possible to prevent oxidation scale.

The reason for removing the oxide film after heating the metal body is as follows.
This is for improving the properties of the product after molding. For removing the oxide film, not only gas such as high-pressure air and nitrogen, but also liquid such as moisture or solid may be used. Further, the reason why the pressure molding is performed while the inserted metal body is in a molten or semi-molten state is that if the metal body solidifies, the fluidity of the metal body deteriorates, and the metal body does not fill the gap 6. It is.

The reason why the mold is pre-heated to 200 ° C. or higher in order to prevent a decrease in the fluidity of the hollow body due to a decrease in the temperature of the hollow body during pressure molding. The effect is lower at a lower temperature. Because. In addition, the processing speed is 20
The reason for setting it to 0 mm / sec or more is to prevent a decrease in the fluidity of the hollow body due to a decrease in the temperature of the hollow body during pressure molding.
This is because the effect is low at lower temperatures.

When the main forming is performed, if necessary, a load of 30% or more of the maximum load during forging is maintained at the bottom dead center of the forging machine until the surface temperature of the hollow body becomes 800 ° C. or less. This is because the generation of voids inside the metal body is suppressed. The reason why the surface temperature of the hollow body is set to 800 ° C. or less is as follows.
This is because the generation of holes is suppressed under this condition. If the holding load is less than 30% of the maximum load at the time of forging, the suppression of vacancies becomes insufficient.

[0014]

Embodiments of the present invention will be described below. Example 1 As an example of the method of the present invention, FIGS. 1 (a), (b) and (c)
The molding was performed according to the steps shown in FIG. A hollow cylindrical body 1 (outer diameter φ40 mm, height 60 mm) is formed from a steel sheet A of steel shown in Table 1 and a metal body B of B is inserted into the hollow body, and is heated to 5 to 20 ° C. by high frequency heating. 1250 ° C at a heating rate of / sec
Was heated. The heating conditions were controlled by a thermocouple embedded in the center of the thickness of the hollow body.

[0015]

[Table 1]

The temperature of the surface layer was also measured simultaneously with a thermocouple. The heating temperature shown in Table 2 is an average value of the temperature at the center of the thickness of the hollow body and the surface layer temperature at this time.

[0017]

[Table 2]

Thereafter, FIG. 1 preheated by high frequency
Pressure was applied in the mold having the shape shown in FIG. For comparison, a single material was molded using solid shapes of steel types A and B (outer diameter φ40 mm, height 60 mm) (Comparative methods 1 and 2). From Table 2, the processing load is 50.0 tonf or less in all of the methods of the present invention. On the other hand, the comparative method 3 in which the thickness of the hollow body is thick, the comparative method 5 in which the heating temperature is low, the comparative method 6 in which the mold preheating temperature is low,
In Comparative Method 7 in which the processing speed during forging is slow, the processing load is larger than 50.0 tonf in each case, and it can be seen that there is a remarkable difference in the formability. In Comparative method 2, the metal body was scattered and molding was not possible.

Further, the loss coefficient (damping coefficient when measuring the vibration damping characteristics of the steel sheet) is 0.024 or more in each of the methods of the present invention. It can be seen that it is significantly larger than that of FIG. Further, when comparing the thickness of the oxide film after forging, the thickness of the oxide film reached 38 μm or less in the method of the present invention, whereas the thickness of the oxide film reached 71 μm in Comparative method 4 in which the heating rate was low.

Example 2 Table 3 shows the results of an examination of the product accuracy after forging and holding the load to 50% of the maximum load during forging.

[0021]

[Table 3]

Table 3 shows the results in the case where the steel type, the heating conditions and the forging conditions were all the same as in Example 1 of the present invention 4 and the forging load was 35 tonf.
Under each condition, 20 pieces were forged, and after cooling, formation of internal pores was observed. Table 3 shows that no voids were found in any of the cases in the method of the present invention, whereas voids were generated in the comparative method, and the voids could be suppressed by the method of the present invention. You can see that.

[0023]

According to the present invention, a high-strength material is used for the outer surface in forming a complex-shaped part which is a characteristic of bath forging.
It is possible to easily form a product using a metal body having excellent vibration damping properties inside.

[Brief description of the drawings]

FIG. 1 is a view showing a composite bath forging method used in an embodiment of the present invention and an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Hollow body 2 ... Metal body 3 ... High frequency heating coil 4 ... Oxide film removal device 5 ... Dice 6 ... Punch 7 ... Void portion 8 ... Heating device 9 ... Product

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-339557 (JP, A) JP-A-4-367362 (JP, A) JP-A-6-190535 (JP, A) JP-A-5-190535 131260 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) B22D 19/00 B22D 18/02

Claims (2)

(57) [Claims] 1. A steel material having a carbon content of 0.1% or more and less than 2% by weight% is formed in advance into a simpler shape than the product shape, and its thickness / mass outer diameter ratio is 0.1%. 2
After inserting graphite cast iron, gray cast iron or alloy cast iron excellent in vibration damping properties into the hollow body within 0, the melting point of the inserted metal body -50 ° C is the lower limit, and the melting point of the hollow body -20 ° C is the upper limit. After high-frequency heating at an average heating rate of 5 ° C./second or more and 20 ° C./second or less in the temperature range, the oxide film was removed,
While the inserted metal body is in a molten or semi-molten state,
Average 2 in a mold preheated to 200 ° C or higher
A method for producing a forged part having excellent vibration damping characteristics, comprising applying pressure at a processing speed of at least 00 mm / sec, molding into a product shape, and solidifying. 2. After the main forming, at the bottom dead center at the time of forging, a load of 30% or more of the maximum load at the time of forging is maintained until the surface temperature of the hollow body becomes 800 ° C. or less.
The manufacturing method as described.