JPH03107418A - Production of gear - Google Patents

Abstract

PURPOSE:To easily and surely produce the gear having excellent fatigue strength and pitting resistance by subjecting the gear to shot peening which project shot particles of specific particle sizes from the tip side toward the deddendum side prior to a surface hardening treatment after tooth working. CONSTITUTION:A rough shape material obtd. by cutting and forging of a material is subjected to the tooth working and is then subjected to the surface hardening treatment, such as carbonitriding, to obtain the gear 1. The formed teeth 2 are subjected to the shot peening prior to the above-mentioned surface hardening treatment after the tooth working in the above-mentioned process for producing the gear. The shot particle size is specified to a 0.2 to 0.6mm range, The direction for projecting the shot particles is so determined that the particles are directed from the tip side toward the deddendum side approximately along the surface of the teeth 2 as shown by arrow and the shot peening is executed while this direction is move in the tooth lead direction. Tip edges 3, shaving steps 4 and hobbing traces, etc., are removed or are changed to adequate shapes in this way, by which the fatigue strength and pitting resistance of the gear are additionally improved.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for manufacturing gears.

(Prior Art) In the manufacture of gears, such as transmission gears, in order to improve fatigue strength and pitting resistance,
After tooth processing, surface hardening treatments such as carburizing and quenching and carbonitriding are carried out, and in addition,
As shown in Publication No. 2, shot peening is performed after surface hardening treatment.

(Problems to be solved by the invention) However, in recent years, there has been a need to further improve fatigue strength and pitting resistance.
A detailed investigation into the manufacturing of gears revealed that the tooth tip edges, shaving steps, bobbing marks, etc. that are formed during gear machining before surface hardening treatment remain even after the assembly is completed.
It has been revealed that these impede improvements in fatigue strength and pitting resistance.

In other words, the tooth edge can scratch the tooth surface of the mating gear, cause high blood pressure and cause abnormal wear, or cause pitting due to carburized parts.
It has been found that shaving steps create notches and reduce bending fatigue strength, and hobbing marks create notches that reduce bending fatigue strength and increase local surface pressure, causing abnormal wear. .

As a countermeasure against this, it is possible to use shot peening during the manufacturing process mentioned above to increase the projection force and shot hardness to remove the tooth tip edges, or to perform grinding before surface hardening treatment. Conceivable. But in the former case.

This will cause the shot particles to break and lead to a decline in productivity.
In addition, shot peening is also performed on tooth surfaces other than the relevant portions, such as tooth tip edges, and the tooth surfaces are more seriously damaged.

Furthermore, in the latter case, the southeastern shape is complex and polishing is extremely difficult and impractical.

The present invention has been made in view of the above circumstances, and its purpose is to further improve the fatigue strength and pitting resistance of gears simply and reliably.

(Means and effects for solving the problem) In order to achieve the above object, the present invention provides a method for manufacturing a gear in which a surface hardening treatment is performed after tooth processing. Before the surface hardening treatment, the shot particle diameter is set to a range of 0.2 to 0.6 mm on the tooth, and the shot particle projection direction is directed from the tooth tip side to the tooth root side approximately along the tooth surface. This is the configuration in which shot peening is performed.

With the above configuration, shot peening is performed with a shot particle diameter of 0.2 to 0.6 mm after tooth processing and before surface hardening treatment, resulting in a product that is softer than that after surface hardening treatment. By performing shot peening under appropriate conditions, it is possible to accurately remove tooth tip edges, shaving steps, and hobbing marks, or change the shape to an appropriate shape with relatively small processing force. . Here, the shot particle diameter is set to 0.2 to 0.6 mm.
To be more specific, it was set in the range of 0.2
If it is less than 0.6 mm, the force of 71L1m is small (it takes a long time to remove or improve the shape of relatively deep machining marks such as hobbing marks, which is unfavorable in terms of production, and if it exceeds 0.6 mm, the machining This is because the force is large and the south side may become matte, which may impair bending fatigue strength and pitting resistance.

Moreover, in this case, since the shot particle projection direction is directed approximately along the tooth surface from the tooth tip side to the tooth root side, the shot particles are projected from the south side of the tooth tip, shaving steps, hobbing marks, etc. This means that shot peening is suppressed, and severe damage to the tooth surface can be minimized.

Therefore, the fatigue strength and pitting resistance of the gear can be further improved in the cylinder and precisely.

(Example) Embodiments of the present invention will be described below based on the drawings.

The gear according to the embodiment of the present invention is manufactured according to the manufacturing process shown in FIG.

11) That is, first, the steel material is cut, and then subjected to a hot forging process and a normalizing process (carried out depending on the case).
to undergo. The conventional process is known, and general conditions are used in each step. Therefore, these details will be omitted.

(2) Next, perform tooth processing.

The reason for performing tooth processing here is that if it were performed after the surface hardening treatment in the post-process, the steel material would be extremely hard (making it difficult to perform tooth processing).

In this case, in this step, as shown in FIGS. 2 and 3, the gear 1 is formed into a gear 1 having a precise dimension and shape. Hobbing marks 5 and the like are formed toward the tooth trace direction.

(3) Next, set the shot particle diameter to a range of 0.2 to 0.6 mm, and change the shot particle projection direction from the tip side to the root side approximately along the tooth surface as shown by the arrow in Figure 2. Perform shot peening while moving in the direction of the tooth trace.

This is done to remove the tooth tip edge 3, shaving step 4, and hob pressure mark 5, or to make the shape appropriate.

The shot particle size is specified by the tooth tip edge 3.
This is because, among the shot peening conditions, the shot particle diameter is the most important factor in revising the calendar.

The reason why the shot particle size is set to be in the range of 0.2 to 0.6 mm is because, as described in detail above, this range is most effective in achieving the object of the present invention.

The reason why the direction of shot particle projection was made to go from the tooth tip side to the groove root side approximately along the south face as shown by the arrow in Fig. 2 is to direct the shot particles of shot peening to the tooth tip edge as much as possible. This is to avoid contacting the tooth surface other than the corresponding location such as No. 3, and to reduce strong damage to the tooth surface.

Shot peening is performed while moving the shot particle projection direction in the tooth trace direction because the tooth tip edge 3 and the shaving step 4 extend in the tooth trace direction.
As shown in Fig. 3, the hobbing marks 5 are formed sequentially in the direction of tooth shedding.
This is to correct these problems by shot peening.

(4) Next, perform surface hardening treatment.

This is done to harden the tooth surface of the gear and increase its fatigue strength.

Examples of surface hardening treatments include carburizing and quenching, carbonitriding, etc.
(including tempering).

(5) Next, shot peening is performed if necessary.

This shot peening is different from the purpose of the shot peening in the previous process, and is performed to create compressive residual stress in the gear to further increase fatigue strength. Conditions for this shot peening are used in accordance with the above purpose and are known.

By going through each of these steps, the manufactured gear has better fatigue strength and pitting resistance.

In order to confirm the effects based on the manufacturing method described in 1., a gear fatigue test was conducted on some test examples.The gear fatigue test was carried out by meshing the test gear with a loaded gear to which a constant load was applied. The number of cycles (number of rotations) until failure was measured, and fatigue strength was determined from this.Specifically, the test conditions for this gear fatigue test are as follows.

[Δ] h test test device Test conditions ■ Test gear (i) Material: SCM420H (ii) Gear type: Secondary pinion gear Module: 2.25 Number of teeth: 18 Face width: 40 mm ■ Shot peening before surface hardening treatment ( i) Shot hardness: HRC35 (ii) Shot particle projection speed: 54 m/sec (ii) Projection distance: 100 mm (to the tooth bottom) ■Surface hardening treatment Surface hardening treatment includes carburizing, quenching, and tempering. use

In carburizing and quenching, the temperature is maintained at 930 Tl for 2.5 hours, the temperature is lowered to 840° C., maintained in that state for 0.5 hours, and then rapidly cooled.

During tempering, the temperature is maintained at 170°C for 2 hours.

■ Load load of load gear in fatigue test: 60.9 kgf-m [B] Unique test conditions for each test example The unique test conditions for each test example are as shown in Table 1. Shot peening before surface hardening treatment and shot peening after surface hardening treatment.

■ Table 1 1 As a result of such a test, the contents shown in Table 2 were obtained.

Table 2 According to the contents shown in Table 2, compared to comparative example 1, present example 1
-4, the fatigue strength (number of cycles until failure) was significantly improved. This is because the shot peening before the surface hardening process rounds the tooth tips, reducing tooth surface scratches, smoothing out the convexities left by hobbing, and reducing stress concentration.
This is considered to be the overall effect of removing or deforming the shaving step to create a smooth shape and reducing stress concentration.

Furthermore, it is thought that the fact that the shot peened tooth surface has a surface roughness with no directionality is also considered to be a contributing factor.

Comparative Example 2 is a case in which shot peening was performed after surface hardening treatment, and in this case, it showed considerably greater fatigue strength than Comparative Example 1 in which shot peening was not performed after surface hardening treatment. However, when shot peening was performed before and after the surface hardening treatment as in Example 4, the fatigue strength was greater than that of Comparative Example 2. This is because the shot peening before the surface hardening process makes the surface of the tooth surface uneven, so if shot peening is performed after the surface hardening process, the shot particles hit the convex parts of the unevenness of the tooth surface, resulting in a higher compression residue. This is thought to be due to the formation of stress. In addition, in this case, it is thought that the fact that the tooth surface has surface roughness with no directionality also contributes.

Furthermore, according to Examples 1 to 3 and Comparative Example 3.4, the shot particle diameter of shot peening before surface hardening treatment was 0.2.
It was shown to be effective in the range of ~0.6 mm.

(Effects of the Invention) As described above, the present invention can further improve the fatigue strength and pitting resistance of gears easily and reliably.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a manufacturing process according to an embodiment of the present invention, FIG. 2 is an explanatory diagram illustrating teeth formed in a tooth processing process, and FIG. 3 is a perspective view of FIG. 2. 1...Gear 2...Tooth Diagram 2

Claims (1)

[Claims] (1) In a method for manufacturing a gear in which a surface hardening treatment is performed after tooth machining, after the tooth machining and before the surface hardening treatment, a shot particle size of 0.2 to 0. 6 mm, and shot peening is performed in a direction in which shot particles are projected approximately along the tooth surface from the tooth tip side to the tooth root side.