JP3000838B2 - Manufacturing method of austempered ductile cast iron gears - 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 an austempered ductile cast iron gear.

[0002]

2. Description of the Related Art Austempered ductile cast iron gears used for timing gears and the like of vehicle engines have conventionally been known.
It was manufactured by any of the manufacturing methods shown in FIGS.

[0003] In the conventional manufacturing method shown in FIG. 4 described above, a suitable spheroidal graphite cast iron (for example, JIS G5502) is used.
1) a gear material is manufactured by the FCD 500 specified in the above), a gear cutting is performed on the material by bob cutting or another appropriate gear cutting method, and a shaving and finishing of the tooth surface is performed. And a third step of subjecting the machined gear to heat treatment (hereinafter referred to as ADI processing).

[0004] The ADI process is a so-called austempering process, in which a gear material is heated to an appropriate temperature above the Ac3 transformation point or the Ac1 transformation point (hereinafter referred to as a first predetermined temperature) for a suitable time (hereinafter referred to as a first predetermined temperature). By maintaining the material, the ground structure of the material is changed to an austenitic structure, then the transformation is stopped as it is, and the ferrite and pearlite formation temperature Ar 'or lower and the martensite formation temperature A
By immersing in a metal bath or a salt bath at an appropriate temperature of r ″ (MS point) or higher (hereinafter referred to as a second predetermined temperature) or a salt bath for an appropriate time (hereinafter referred to as a second predetermined time) and cooling, the ground structure of the material is reduced. This is a treatment method of forming a bainite structure and then cooling in the air.

In the ADI process, when the second predetermined temperature is close to Ar ′, a soft upper bainite structure is formed, and when the second predetermined temperature is close to Ar ″, a hard lower bainite structure is formed.

In the conventional method of manufacturing a granular graphite cast iron gear shown in FIG. 4, since the gears that have been precisely finished by shaving after gear cutting in the above step 2 are subjected to heat treatment (ADI processing). However, there is a disadvantage that the deformation due to the heat treatment is large and the accuracy is deteriorated.

Next, in the conventional manufacturing method shown in FIG. 5, a step 1 'of casting a gear material with the same granular graphite cast iron as described above.
And a step 2 'of subjecting the cast gear material to the same ADI processing as described above, and a machining step 3 of performing a gear cutting such as bob cutting on the gear material after the heat treatment and then performing shaving to perform precision finishing of the tooth surface. '.

In this manufacturing method, since the machining allowance for hobbing or the like of a gear material after ADI processing is extremely large, work hardening occurs and machinability is greatly deteriorated, and cutting is extremely difficult or difficult. In the worst case, cutting becomes impossible, and there is a problem that it is difficult to perform cutting within a practically acceptable cost range.

[0009]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for manufacturing a gear made of austempered ductile cast iron having excellent strength and toughness at a low cost while ensuring high accuracy. It is assumed that.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in order to achieve the above object, and comprises a first step of gear cutting a spheroidal graphite cast iron material to form a gear coarse material. At a first predetermined temperature, a first gear is used to austenize the gear coarse material.
Hold for a predetermined time, and then use the second
A second step of gradually cooling after holding at a predetermined temperature for a second predetermined time, and a third step of forming a gear by shaving the tooth surface of the above-described coarse gear material that has been subjected to the heat treatment of the second step. The present invention proposes a method for producing an austempered ductile cast iron gear.

[0011]

According to the present invention, in the first step, the gear material made of spheroidal graphite cast iron is subjected to gear cutting such as hobbing to form a gear coarse material, and then in the second step, the gear coarse material is subjected to AD.
I processing is performed, and shaving finish processing of the tooth surface is performed in the last third step. Since the gear material before the ADI processing has good machinability, the gear cutting in the first step is easily performed. In the second step of performing the ADI treatment on the gear blank after the gear cutting, the second predetermined temperature for the above-mentioned bainite is set slightly higher than usual, and the temperature difference from the first predetermined temperature for the austenitization is reduced. By doing so, an upper bainite structure capable of ensuring excellent toughness and high tensile strength is generated, and the amount of deformation by heat treatment can be sufficiently reduced. In the third step, the gear tooth surface is subjected to shaving finish. At this time, the shaving finish allowance is obtained by adding the finishing allowance of the gear cutting in the first step and the heat treatment deformation amount in the second step. In addition, since the amount of heat treatment deformation is suppressed to a small value, shaving is performed smoothly, and a high-precision gear can be obtained.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be specifically described below with reference to FIGS. First, in the process diagram of FIG. 1, reference numeral 10 generally indicates a manufacturing process of the method of the present invention, 12 is a cast gear material, 14 is a first step of performing hobbing or the like on the gear material 12, Reference numeral 16 denotes a second step of applying ADI processing to the gear-cut gear blank, 18 denotes a third step of applying a shaving finish to the tooth surface of the ADI-treated gear, and 20 denotes shaving as desired. The fourth step of performing shot peening on the tooth surface of the finished gear is shown.

The gear material 12 is made of a suitable granular graphite cast iron, preferably, F steel specified in JIS G5502.
Manufactured by CD700. The gear material 12 in the as-cast state usually has a microstructure composed of granular graphite, ferrite mainly precipitated around graphite, and pearlite, and has a tensile strength σ _B of approximately 60 to 70 kg / mm ² ,
In about 250 hardness _{H B,} it is excellent machinability.

Next, the gear material 12 is subjected to a first step 14
In this case, hobbing is performed, but gear cutting is performed before the heat treatment is performed in the as-cast state of the gear material. Therefore, the processing is performed easily and a gear coarse material is formed.

For example, the gear coarse material after the gear cutting is subjected to the AD of the second step according to the temperature-processing time diagram of FIG.
I processing is performed. That is, the above-mentioned gear coarse material is first A ₁
The temperature is increased to a first predetermined temperature T ₁ (which is appropriately set within a temperature range of 830 ° C. to 900 ° C.) which is equal to or higher than
The first predetermined time _{h 1} (e.g. 1 hour) to ₁ is maintained. In the illustrated, the gear coarse material is gradually heated spent 0.5 hours to reach the first predetermined temperature T ₁ of from room temperature. By holding the first predetermined time, the first predetermined temperature T _1, foundation structure consisting of a ferrite and pearlite gears coarse material is austenitic structure.

The gear coarse material having an austenite structure as described above prevents the transformation of the gear coarse material and maintains the second ferrite and pearlite formation temperature Ar ′ or lower and the marcite formation temperature Ar ″ (MS) or higher. Predetermined temperature T
_{2 is} immersed in a metal bath or a salt bath maintained at, for example, 370 ° C. close to Ar ′ for a second set time h ₂ (for example, 1 h), cooled, then taken out of the bath and allowed to cool in the air. By the second set time h ₂ held by the second predetermined temperature T _2, the ground structure of the gear coarse material is changed to the upper base Knight tissue, comprising the toughness of the steel material comparable, and the tensile strength sigma _{B =} 90 to 110 kg / mm ^2, excellent mechanical properties before and after the hardness _H a = 300 is obtained. An example of the salt bath is a mixed salt of potassium nitrate and sodium nitrate having a melting point of about 140 ° C. and a density (at 300 ° C.) of 1.8 g / cm.
^3. Those having a working temperature range of 160 ° to 550 ° C. are advantageously used.

Shaving is performed on the tooth surface of the gear coarse material that has been subjected to the above-described ADI processing, and a high-precision gear of second to third grade or higher according to JIS is obtained. The finishing allowance for shaving is, of course, the sum of the finishing allowance remaining after the gear cutting in the first step and the heat treatment deformation caused by the ADI processing in the second step.
In the I treatment, following the austenitizing treatment at the first predetermined temperature T ₁ , the second predetermined temperature T ₂ that is rapidly cooled to be a bainite structure is set to a temperature close to Ar ′, and the difference from the first predetermined temperature T ₁ is determined. By reducing the size, the residual stress of the gear material can be reduced and the amount of deformation can be reduced. In particular, F has a low ferrite ratio in the as-cast ground structure and a large pearlite structure.
For gear material consisting CD600～FCD700, hitting the austenitizing at the first predetermined temperature T _1, from the volume increase rate accompanying the transformation from ferrite structure to austenitic structure, due to the transformation from pearlite structure to austenitic structure Since the volume increase rate is sufficiently small, the amount of heat treatment deformation during the ADI process can be further reduced. As a result, the shaving finish allowance can be kept within the range of 0.05 to 0.1 mm. With the finish allowance in this range, excellent productivity can be secured without impairing the durability of the shaving tool. However, a high-precision gear can be obtained at low cost. In addition, this finishing process generates residual stress due to work hardening on the surface, improves pitting resistance, and improves gear fatigue strength. Therefore, when this gear is used, for example, as a timing gear of a vehicle engine, there is an advantage that it is possible to effectively reduce the meshing noise in combination with the excellent damping characteristics inherent in cast iron and high accuracy.

Next, shot peening in a fourth step is performed on the tooth surface of the gear that has been subjected to the above-mentioned shaving, as necessary. Shot peening is a working degree capable of increasing the surface hardness without lowering the precision of the tooth surface to achieve an improvement in wear resistance and an improvement in fatigue strength, preferably in the range of 0.15 to 0.30 mm arc height. I do. At this time, it is also possible to apply an appropriate masking to the meshing tooth surface other than the tooth root, and to apply shot peening only to the tooth root particularly requiring fatigue strength.

Further, prior to the gear cutting in the first step, the gear blank 12 can be subjected to preliminary normalization (hereinafter referred to as N treatment) as necessary. N above
As shown in FIG. 3, the treatment is performed by heating the gear blank 12 to an appropriate temperature T ₃ (for example, 860 ° C.) of the transformation point A ₁ or higher and an appropriate time h ₃ (for example, 1 hour or more) of about 10 minutes to 1 hour. After the holding, cooling is performed to remove the distortion and the residual stress of the gear material. By performing this process, the machinability of the gear cutting in the first step can be further improved. Further, by performing this treatment, the ferrite structure in the ground structure is transformed into an austenite structure, and almost all of the structure becomes a pearlite structure upon cooling. Therefore, the heat treatment deformation in the ADI treatment (second step) after the gear cutting is performed. It can be even smaller. This means that the volume increase when the ferrite structure contained in a considerable amount in the ground structure of the gear material 12 is transformed into the austenite structure in the ADI processing as described above is large, and the ground processing is performed by the N processing. By changing the pearlite structure in the ferrite structure in advance, the pearlite structure is transformed into an austenite structure in the ADI treatment.
This is due to the fact that the amount of change in volume can be suppressed small. As a result, there is an additional advantage that the finishing allowance in the shaving processing in the third step can be further reduced, the processing speed can be increased, and the processing cost can be further reduced.

[0020]

As described above, the method for manufacturing an austempered ductile cast iron gear according to the present invention is a first step of gear cutting a spheroidal graphite cast iron material to form a gear coarse material. A second step of holding the coarse material at a first predetermined temperature for a first predetermined time for austenitization, further holding a second predetermined temperature at a second predetermined temperature for an upper bainite for a second predetermined time, and then gradually cooling the same; Forming a gear by shaving the tooth surface of the gear coarse material having been subjected to the heat treatment
And has the advantage that a highly accurate ductile cast iron gear having excellent toughness and tensile strength and high accuracy can be provided at a low cost.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a gear manufacturing process of the present invention.

FIG. 2 is a diagram showing a second step (ADI processing) of the present invention.

FIG. 3 is a diagram showing N processing performed as necessary on the gear material of the present invention.

FIG. 4 is a flowchart showing a manufacturing process of a conventional ductile iron gear.

FIG. 5 is a flowchart showing another manufacturing process of the conventional ductile iron gear.

[Description of Signs] 12 Gear Material 14 First Step 16 Second Step 18 Third Step

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B23P 15/14 C21D 9/32

Claims (1)

(57) [Claims] A first step of gear cutting a spheroidal graphite cast iron material to form a gear coarse material; holding the gear coarse material at a first predetermined temperature for a first predetermined time for austenitizing;
Further, a second step of holding at a second predetermined temperature for a second predetermined time for upper bainizing and then gradually cooling, and shaving the tooth surface of the gear coarse material subjected to the heat treatment of the second step to form a gear, A method of manufacturing an austempered ductile cast iron gear, comprising a third step of forming.