JPH03196970A - Shot peening method for gear - Google Patents

Abstract

PURPOSE:To give a tensile preload to all the bottom uniformly at a time by applying a shot-peening process to the bottom part of a gear in the state that the tensile preload is given to the bottom of the gear in the profile direction after imposing internal pressure onto the diametral direction from a cylindrical gear inner surface. CONSTITUTION:An expander 7 adds force to a cylindrical gear a gear of a shot-peening workpart 2 from the cylinder inside to the outside. In a state of making the tensile load act on a gear circumferential direction of the cylindrical gear 2 by this expander 7, shot-peening particles 3 are impacted against a tooth bottom of the gear 2 in use of centrifugal force of a rotor whereby a shot-peening process takes place.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for improving the fatigue strength of gears, and more particularly to a shot peening method for gears that forms even higher residual compressive stress on the tooth root surface of the gear. .

(Prior Art) As a conventional method for shot peening a gear, there is a method as shown in FIG. 2, for example. FIG. 2 is a plan view of a conventional shot peening method, in which a gear 2, which is an object to be shot peened, is placed on a rotary table 1. The gear 2 rotates or revolves together with the rotary table 1. The shot peening particles 3 are mainly composed of metal particles, and are projected onto the gear 2 using the centrifugal force of the rotor or high-speed airflow. Shot peening treatment is performed for the purpose of forming high residual compressive stress on the surface of the object to be processed by plastically deforming the surface of the object to be processed. This greatly contributes to improving the fatigue strength of When considering improvement in fatigue strength, the higher the residual compressive stress, the better. To this end, as shown in FIG. 2, various measures have been taken other than simply subjecting the gear to shot peening. For example, there is a method as shown in FIG. 3 (Japanese Unexamined Patent Publication No. 178176/1983).

In FIG. 3, an opening jig 4 is used to push open the gap between two adjacent gears, and a through hole 5 is provided in the portion facing the bottom of the tooth. - The convex part 6 of the opening jig 4 is provided so as to correspond to the opening jig 4.
By applying shot peening to the tooth bottom of the gear 2 from the hole of the through hole 5 while applying tensile stress to the tooth bottom, the tooth bottom has an even higher residual compressive stress. (Problem to be Solved by the Invention) However, in such conventional shot peening treatment methods for gears, higher residual compressive stress is applied to the bottom of the tooth of the gear. If you try to do this, the jig configuration will become complicated, and when the shot particles are projected onto the shot peening target, the particles will interfere with each other, reducing the reliability of the process, which will complicate the work process and reduce productivity. significant decline,
There were problems such as large variations in strength, which made it impractical for practical use.

(Means for Solving the Problems) The present invention has been made by focusing on such conventional problems, and in a shot peening treatment method for cylindrical gears, internal pressure is applied in the diametrical direction from the inner surface of the gear cylinder. By applying a shot peening treatment to the tooth root of the gear while applying a tensile preload in the force direction of Kmm to the tooth root,
The purpose is to solve the above problems. FIG. 1 is a diagram showing an embodiment of the present invention. The expander 7 is capable of applying force to the cylindrical gear 2, which is the gear of the object to be shot peened, in a direction from the inside of the cylinder to the outside of the cylinder. By applying a tensile load to the cylindrical gear 2 in the circumferential direction of the gear by the expander 7 in this manner, the shot peening particles 3 are made to collide with the bottom of the gear 2 using the centrifugal force of the rotor. Shot peening treatment was performed. The gear 2 was placed on a rotary table 1 together with the expander 7, and subjected to shot peening treatment while being rotated.

Specifically, the gear 2 is a cylindrical gear with a module of 1.5, and the material is SCr 420 steel subjected to gas, carburizing, quenching and tempering treatment, and the effective hardened layer depth at the tooth bottom is 0.5.
It was m. The shot peening particles 3 are steel balls having a hardness of HRC53 and a diameter of 0.5u.

The shot peening treatment conditions were an arc height of 0.7 and a coverage of 500%. Note that the gear was rotating during the shot peening treatment, and the rotation speed was 4 rpm. The tensile stress in the tooth root profile direction due to the expander is 50 kl
/f 7mm”.

For comparison, a gear under the same conditions as this gear was also subjected to conventional shot peening treatment without applying root tensile stress using an expander.

A gear subjected to shot peening treatment according to the present invention,
A power cycling fatigue test was conducted on gears that had been shot peened using a conventional method. The results of the fatigue test are shown in Figure 4. As shown in FIG. 4, it can be seen that the shot peening method according to the present invention has a higher fatigue strength by about 10% than the conventional shot peening method. As a matter of course, the inner pressure of the gear cylinder may be within the elastic limit (although there is no particular restriction).

Furthermore, there are various types of devices that apply the pressure inside the gear cylinder, including hydraulic, spring, and mechanical devices, and these are not particularly limited.

(Effects of the Invention) As described above, according to the present invention, in the shot peening method for a cylindrical gear, internal pressure is applied in the diametrical direction from the inner surface of the gear cylinder to apply a tensile preload to the tooth bottom of the gear in the tooth profile direction. Since the shot peening process is applied to the im part of the gear in the same state, the jig structure does not inhibit the collision movement of the shot peening particles. A tensile preload can be applied, there is almost no decrease in work efficiency, and the fatigue strength can be further increased.

[Brief explanation of drawings]

Figure 1 shows the shot peening method for gears according to the present invention, in which shot peening is applied to the tooth bottom with a tensile preload applied. Figure 2 shows the most common conventional shot peening method for gears. Figure 3 shows the most common conventional shot peening method for gears. Figure 4 shows a conventional shot peening treatment method in which shot peening treatment is performed with a tensile preload applied to the tooth bottom, and Figure 4 shows fatigue test results of gears subjected to shot peening treatment according to an example of the present invention and a comparative example. It is. l... Rotary table, 2... Gear, 3... Shot peening particles, 4... Opening jig, 5... Through hole, 6... Convex portion, 7... Expansion machine.

Claims (1)

[Claims] (1) In the shot peening method for cylindrical gears, shot peening treatment is performed on the tooth bottom of the gear while applying internal pressure in the diametrical direction from the cylindrical inner surface of the gear and applying a tensile preload to the tooth bottom in the tooth profile direction. A method for shot peening gears.