JPH10202435A - Helical gear manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve abrasion resistance and pitching strength along the overall length of face width by forming a hardened layer along a tooth profile by applying high frequency quenching on a face of tooth of a gear machined to have the face width larger than finishing dimensions and removing a non- uniform hardened layer by cutting both end parts in the face width direction thereafter. SOLUTION: As a result of high frequency quenching, a hardened layer 20 is formed on the whole of a face of tooth from an addendum of a tooth 12 to a dedendum, and the hardened layer 20 is formed thick at an addendum part and relatively thin at a dedendum part. When a gear end surface is cut along lines X1 and X2 , a gear 10 furnished with the tooth 12 having the uniform hardened layer 20 along face width overall length Y of the tooth 12 of the helical gear 10 and consequently excellent in abrasion resistance and pitching strength is manufactured. It is favourable that thickness of the hardened layer 20 at the dedendum part on which the largest bending force works at the time of engagement of the gear is about 0.2-0.4mm.

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 helical gear having excellent wear resistance and bending fatigue strength. Incidentally, in the so-called helical gear of the present invention, a normal gear in which the tooth traces are formed to be inclined with respect to the plane including the rotation axis of the gear, and the rotation axes of the gear pair meshing with each other are parallel to each other. The tooth trace is formed to be inclined with respect to the plane including the helical or helical gear and the rotation axis of the gear, and the rotation axes of the gear pair meshing with each other are in a projection plane parallel to one rotation axis. It includes so-called screw or screw gears that intersect each other.

[0002]

2. Description of the Related Art Gears used in automobiles and the like, which are required to have durability, are prepared by first forming a forged material using steel as a rough material, tempering it, and then using a hob or another gear cutting tool. It is common practice to cut and then perform a carburizing heat treatment to form a hardened layer with excellent wear resistance on the tooth surface.

When a helical gear is manufactured by the above-described normal manufacturing method, as shown in FIG. 7 which shows a sectional view of a tooth along a pitch circle, as shown in FIG. 2, the thickness Da of the hardened layer 2a on the acute angle side of the inclined tooth 1, the thickness Db of the hardened layer 2b on the obtuse angle side, and the thickness Dc of the tooth surface hardened layer 2c at the center of the tooth width. Are greatly different, as an example, Da is about 1.6 mm, Dc is 0.6 m
m, Db of the obtuse angle portion has an intermediate thickness between Da and Dc.

A helical gear subjected to the above-mentioned carburizing heat treatment is disadvantageous in strength because the thickness Da of the carburized hardened layer 2a on the acute angle side of the tooth 1 is excessively large, and has a small heat capacity as compared with other parts. When the tooth contact occurs on the acute angle side where the strength tends to decrease, there is a possibility that the contact may be broken starting from the acute angle side.

[0005] In order to solve the above-mentioned problems of the conventional gear manufacturing method, the material gear is cut with a torsion angle of the teeth of the finished gear, that is, a torsion angle larger than the normal torsion angle, and then carburized according to a conventional method. A method has been already proposed in which a carburized hardened layer is formed on the tooth surface by heat treatment, and then the carburized hardened layer is further ground by shaving to form a tooth having a regular helix angle. (See Japanese Unexamined Patent Publication No. 7-54967; hereinafter, this helical gear manufacturing method is referred to as a previously proposed method.)

[0006] In the above-mentioned proposed manufacturing method, the cutting allowance of shaving is essentially extremely small (for example, 0.04 to 0.06 mm with gears of modules 1.5 to 2.0,
0.06 to 0.09 with module 4.0 to 5.0 gears
mm), the thickness Da of the hardened layer 2a on the acute angle side of the tooth 1 is about 1.6 like the above-mentioned helical gear.
mm, when the thickness Dc of the hardened layer in the central portion 2c is 0.6 mm, it is essentially difficult to cut the hardened layer having a high hardness by removing a cutting allowance of about 1.0 mm by shaving. In addition to the above, a large number of processing steps are required, so that there is a disadvantage that the manufacturing cost is significantly increased. Moreover, since the hardened layer 2 is formed on the tooth surface by the normal carburizing heat treatment, there is a disadvantage that the compressive residual stress at each part of the tooth surface is small and the bending fatigue strength is insufficient.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. Compared with the above-mentioned proposed method, the processing is extremely easy, the manufacturing cost is very low, and the compression of each part of the tooth surface is reduced. It is an object of the present invention to provide a method for manufacturing a helical gear having a large residual stress and excellent bending fatigue strength.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an induction hardening method for a tooth surface of a gear which is gear-cut so as to have a tooth width larger than a finished dimension and hardens the tooth surface along the tooth profile. A method for manufacturing a helical gear is proposed in which a layer is formed, and thereafter, both ends in the tooth width direction are cut to remove a non-uniform hardened layer. According to the above manufacturing method, the hardening treatment of the tooth surface is extremely simple and easy, and it is easy to control the thickness of the hardened layer formed on each part of the tooth surface,
Since the time required for the treatment is extremely short, there is an advantage that the production cost is significantly lower than the above-mentioned proposed method.
Furthermore, when induction hardening is performed on inclined teeth, the quenching depth on the acute angle side near the end of the tooth width tends to be larger than the central part of the tooth width, and the quenching depth on the obtuse angle side becomes smaller than the central part of the tooth width. Therefore, the gear width of the gear is formed larger than the regular size in advance, and after induction hardening, both ends in the width direction are cut and finished to the regular size, so that the thickness is substantially uniform over the entire length of the gear width. A helical gear having a hardened layer is obtained, and the wear resistance, pitting strength and bending fatigue strength of the teeth are improved. In addition, in the induction hardening of the tooth surface in the method of the present invention, a thickness of 0.2
It is preferable that a hardened layer having a thickness of about 0.4 mm is formed. By forming the hardened layer having a thickness in this range, a sufficiently large residual compressive stress that is advantageous for improving the bending fatigue strength is generated.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be specifically described below with reference to FIGS. First, FIG.
In the figure, reference numeral 10 is a helical gear having teeth 12 inclined with respect to a plane passing through the rotation axis OO, and 14 is a high-frequency hardening coil disposed coaxially on the outer periphery of the helical gear 10. is there. The coil 14 is connected to a high-frequency oscillator (not shown), and is supplied with a high-energy pulse in an energizing pattern described later.

The helical gear 10 is made of, for example, ordinary carbon steel or spheroidal graphite cast iron having an appropriate composition. For example, in the case of the helical gear 10 using a medium or high carbon steel material, a coarse material cut to an appropriate size is forged, tempered by a conventional method, and then the desired module and inclination angle are adjusted by a hob or another gear cutting tool. The tooth having the shape is cut, and if necessary, shaving is performed to finish the tooth mold. The tooth is finished and attached to the main shaft 16 of the induction hardening device shown in FIG.

[0011] Then, while rotating the spindle 16 at a slow speed,従Gai the bias pattern shown in Figure 4, first, t ₁ seconds, subjected to preheating current of middle frequency AkHz, gear 10 Helical dedendum temperature of the tooth 12 is heated until the T ₁ of the. After that, there is a small pause time (t ₂ −t ₁ ),
(T 3 _{-t 2)} of the short time, high after the dedendum temperature performs main energization frequency BkHz was heated to T _2, the gear during injection or coolant a coolant to the gear 10 Helical It is immersed and quenched to form a hardened layer on the tooth surface from the tip of the tooth 12 to the base of the tooth.

In FIG. 4, preheating time t ₁ , preheating frequency A, root temperature T ₁ , rest time (t ₂ -t ₁ ), main heating time (t ₃ -t ₁ ), main heating frequency B, main heating dedendum temperature T _2, etc. of the time, the material of the gear 10 helical, are set appropriately in accordance with the module or the like of the teeth 12.

As a result of the induction hardening, the helical gear 10
A hardened layer 20 as shown in a satin pattern in FIG. 2, which is a developed cross-sectional view along the pitch circle PCD, is formed over substantially the entire tooth surface from the tip of the tooth 12 to the base of the tooth 12, and FIG. −
As shown in FIG. 3 which is a partial cross-sectional view along the line III, the hardened layer 20 was formed thick at the tooth tip 12a and relatively thin at the tooth root 12b.

Helical gear 10 using medium / high carbon steel
Further, as a result of the induction hardening, the structure of the hardened layer 20 is martensite, and the surface hardness is about 800 in Hv.
It was confirmed that the hardness was sufficient and the wear resistance was excellent. The residual compressive stress of the tooth surface near the pitch circle is approximately 350 to 450 (MPa), and the thickness of the hardened layer 20 at the root where the largest bending force is applied at the time of gear engagement is 0.2 to 0.5. It is preferably about 4 mm, and the residual compressive stress of the root portion is approximately 1000 to 1400 (MP
a) It was confirmed that the material had sufficient bending fatigue strength.

FIG. 5 shows an example of the mode of hardness change in the depth direction of the hardened layer 20 from the tooth surface.
In the figure, the tooth tip 12a indicated by a white triangle hardens to a deep position, and the tooth root 12b indicated by a white circle hardens the hardest, and the pitch circle indicated by a black circle circles: It was found that a hardened layer close to, but slightly larger than, approximately the root portion 12b was obtained.

Further, when the above-described induction hardening is performed on the helical gear 10, as shown in the developed sectional view along the pitch circle in FIG. It was confirmed that the hardened layer 20c on the acute angle side was deepened and the hardened layer 20d on the obtuse angle side was relatively thin or did not harden. When induction hardening is performed on the helical gear, this tendency of the quenching pattern is unavoidable. When the depth or thickness of the acute angle side hardened layer 20c is large, since the heat capacity of the same portion is smaller than the other portion, the strength is easily reduced, and when the tooth contact occurs from the acute angle side tooth surface at the time of meshing. However, there is a possibility that damage will occur from this part. Further, when the depth or thickness of the obtuse angle side hardened layer 20d is small or not hardened, the advantage of surface hardening is of course lost early due to abrasion, or the same as when no hardening treatment is performed. In addition, there is a problem that the wear resistance is impaired and the pitting strength is reduced. On the other hand, if the heating time is extended to increase the thickness of the hardened layer 20d, the depth of the entire hardened layer becomes relatively deep, and there is a disadvantage that a compressive residual stress cannot be obtained.

[0017] Therefore, as shown by the dotted lines _{X 1} and _{X 2} in FIG. 2, and excising the acute angle portion hardened layer 20d and the obtuse portion hardened layer 20d, dimensionally between lines _{X 1} and _{X 2} If Y is previously set to the exact size of the helical gear 10, ie, the normal size, and after the above-described induction hardening, the gear end face is cut along the lines X ₁ and X ₂ , the teeth 12 of the helical gear 10 The helical gear 10 having the teeth 12 having the substantially uniform hardened layer 20 over the entire width Y of the tooth width, and thus having excellent wear resistance and pitting strength is produced. Note that FIG.
In the above, the acute angle side hardened layer 20c and the obtuse angle side hardened layer 20d
The case where the dimensions in the tooth width direction are substantially the same dimension is shown, but the dimensions in the tooth width direction of the hardened layers 20c and 20d differ depending on the inclination angle of the teeth 12, the module, and the conditions of induction hardening. case, leaving no unhealthy quenching moiety, the lines X ₁ and X ₂ be set so as to be removed until hardened layer 20c or 20d having a larger dimension of the tooth width direction is desirable.

FIG. 6 shows a helical gear manufactured by the above-described method of the present invention using the normal steel materials A and B and a steel material SCr420H suitable for carburizing and quenching. This is a comparison of the fatigue limit with the conventional helical gear, and the helical gear according to the method of the present invention has a 25% higher fatigue strength than the conventional helical gear.

The cutting of the gear end face along the X ₁ and X ₂ line is compared to the shaving of the tooth surface which is hardened in the process of the already-proposed, it is easy to remarkably cutting, large cutting costs There is an advantage that the width can be reduced. Furthermore, the induction hardening step in the method of the present invention has an advantage that the cycle time is extremely short and the quenching depth can be easily and accurately controlled as compared with the above-mentioned proposed carburizing heat treatment. Moreover, the carburizing heat treatment typically involves batching a certain number of helical gears simultaneously, and is thus not suitable for continuous flow production. Since insertion and removal, tightening and unscrewing of the nut 18 can all be easily automated, continuous processing can be performed in the gear processing line, and this also has the advantage of reducing manufacturing costs. .

In the above embodiment, a method of manufacturing a helical gear made of medium- and high-carbon steel has been described. However, a spheroidal graphite cast iron having an appropriate composition (for example, C: 2.6 to
4.0%, Si: 1.5 to 3.5%, Mn: 0.20
1.0%, Mo: 0.03 to 0.09%, Cu: 0.1
-0.7%, Mg: 0.005-0.08%, balance iron)
The method of the present invention can also be applied to a helical gear made of, and in any case, the above-described various advantages and effects can be obtained as compared with a helical gear formed by a conventional carburizing heat treatment method. Was confirmed. In addition, the helical gear 10 manufactured by the method of the present invention has a small tooth deformation with a small thermal deformation as a result of short-time induction hardening, and has sufficient tooth form accuracy. The mold may be precisely corrected.

[0021]

As described above, according to the method of manufacturing a gear according to the present invention, the tooth surface of the gear processed to have a tooth width larger than the finished dimension is subjected to induction hardening to form a hardened layer along the tooth profile. Is formed, and then the both ends in the tooth width direction are cut to remove the uneven hardened layer.The wear resistance, pitting strength, and bending fatigue strength are excellent over the entire length of the tooth width, and the manufacturing cost is remarkably high. There is the advantage that a cheap helical gear can be provided. Furthermore, when induction hardening of the tooth surface is performed, a hardened layer having a thickness of 0.2 to 0.4 mm is formed on the tooth root portion. There is an advantage that a residual compressive stress is generated.

[Brief description of the drawings]

FIG. 1 is a plan view of a main part of an induction hardening apparatus for carrying out a method of the present invention.

FIG. 2 is a developed sectional view along a pitch circle of a helical gear which has been subjected to a quenching process by the quenching apparatus of FIG.

FIG. 3 is a partial cross-sectional view along the line III-III in FIG. 2;

FIG. 4 is a thermal cycle diagram when induction hardening of a helical gear is performed.

FIG. 5 is a diagram showing a relationship between hardness of each part of a tooth surface on which induction hardening of a helical gear is performed and depth from a tooth surface.

FIG. 6 is a table showing the fatigue strength of a helical gear manufactured by the method of the present invention and a helical gear subjected to conventional carburizing and quenching.

FIG. 7 is a cross-sectional view along a pitch circle of a conventional helical gear in which carburizing heat treatment is performed on a tooth surface.

[Explanation of symbols]

10: helical gear, 12: teeth, 14: coil for induction hardening, 16: main shaft of the induction hardening device, 20: hardened layer.

Claims (2)

[Claims] 1. A tooth surface of a gear which has been tooth-cut so as to have a tooth width larger than a finished dimension is subjected to induction hardening to form a hardened layer along a tooth profile, and thereafter, both ends in a tooth width direction are cut. A method for manufacturing a helical gear, comprising removing a non-uniform hardened layer. 2. The method for manufacturing a helical gear according to claim 1, wherein a hardened layer having a thickness of 0.2 to 0.4 mm is formed on the tooth root portion by the induction hardening.